Accumulated Other Comprehensive Income (Loss) (Changes in Accumulated Other Comprehensive Loss by Component) (Detail) - USD ($)
$ in Millions

3 Months Ended

6 Months Ended

Jun. 30, 2025

Mar. 31, 2025

Jun. 30, 2024

Mar. 31, 2024

Jun. 30, 2025

Jun. 30, 2024

Accumulated Other Comprehensive Income (Loss) [Line Items]

Accumulated other comprehensive (income) loss, other, after tax, beginning balance

$ (1)

$ 1

$ (1)

$ 1

Accumulated other comprehensive loss, beginning balance

(114)

(131)

(114)

(131)

Other comprehensive income (loss), before reclassifications, net of tax

(2)

Amounts reclassified from accumulated other comprehensive loss:

Amortization of prior service credit

(15)

(27)

Amortization of actuarial loss

Settlement loss

Other

Tax effect

Other comprehensive income (loss)

$ 1

$ (9)

(12)

(21)

Accumulated other comprehensive (income) loss, other, after tax, ending balance

(2)

Accumulated other comprehensive loss, ending balance

(108)

(152)

(108)

(152)

Other comprehensive income (loss) before reclassifications, tax

(1)

Pension Benefits

Accumulated Other Comprehensive Income (Loss) [Line Items]

Accumulated other comprehensive (income) loss, defined benefit plan, after tax, beginning balance

(235)

(261)

(235)

(261)

Amounts reclassified from accumulated other comprehensive loss:

Accumulated other comprehensive (income) loss, defined benefit plan, after tax, ending balance

(224)

(270)

(224)

(270)

Other Benefits

Accumulated Other Comprehensive Income (Loss) [Line Items]

Accumulated other comprehensive (income) loss, defined benefit plan, after tax, beginning balance

$ 122

$ 129

122

129

Amounts reclassified from accumulated other comprehensive loss:

Accumulated other comprehensive (income) loss, defined benefit plan, after tax, ending balance

$ 116

$ 120

116

120

Accumulated Defined Benefit Plans Adjustment | Pension Benefits

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive income (loss), before reclassifications, net of tax

Amounts reclassified from accumulated other comprehensive loss:

Amortization of prior service credit

^[1]

(4)

(16)

Amortization of actuarial loss

^[1]

Settlement loss

^[1]

Tax effect

(2)

Other comprehensive income (loss)

(9)

Accumulated Defined Benefit Plans Adjustment | Other Benefits

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive income (loss), before reclassifications, net of tax

(1)

Amounts reclassified from accumulated other comprehensive loss:

Amortization of prior service credit

^[1]

(11)

Amortization of actuarial loss

^[1]

Settlement loss

Tax effect

Other comprehensive income (loss)

(6)

(9)

Other

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive income (loss), before reclassifications, net of tax

(3)

Amounts reclassified from accumulated other comprehensive loss:

Other

Tax effect

Other comprehensive income (loss)

$ 1

$ (3)

[1]	These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 21.

Marathon Petroleum Corp 10-Q