Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 1
Interest cost	658	669
Expected return on plan assets	(721)	(769)
Amortization of prior service credits	(18)	(19)
Recognized net actuarial loss/(gain)	155	76
Net periodic benefit cost/(income)	76	(42)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	13
Interest cost	30	34
Expected return on plan assets	(3)	(3)
Amortization of prior service credits	(1)
Recognized net actuarial loss/(gain)	(35)	(36)
Net periodic benefit cost/(income)	3	8
Operating Income (Loss) | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in cost/(income) from operations, Other income, net and Earnings/(loss) before income taxes	1	1
Operating Income (Loss) | Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in cost/(income) from operations, Other income, net and Earnings/(loss) before income taxes	12	13
Other Income | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in cost/(income) from operations, Other income, net and Earnings/(loss) before income taxes	74	(43)
Other Income | Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in cost/(income) from operations, Other income, net and Earnings/(loss) before income taxes	(9)	(5)
Operating Income (Loss) Before Taxes | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in cost/(income) from operations, Other income, net and Earnings/(loss) before income taxes	75	(42)
Operating Income (Loss) Before Taxes | Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in cost/(income) from operations, Other income, net and Earnings/(loss) before income taxes	$ 3	$ 8