Postretirement Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Amount by which fair value of plan assets exceeds market-related value of plan assets (MRVA)	$ (7,955)
Derivative net notional amount for fixed income as percentage of total plan assets	42.00%	38.30%
Derivative net notional amount for global equity, currency overlay and commodities as a percentage of total plan assets	0.80%	2.10%
Defined contribution plan, cost	$ 1,670	$ 1,564	$ 1,260
Pension
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation (ABO) for all pension plans	49,889	53,671
Defined benefit plan, plan assets, amount	$ 45,574	$ 48,891	49,825
Defined benefit plan, actual plan asset allocations	100.00%	100.00%
Pension | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	59.00%	60.00%
Pension | Equity securities:
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	19.00%	19.00%
Pension | Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 6,525	$ 5,950
Pension | Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	213	226	268
Pension | Corporate | Level 3 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets Level 3 reconciliation, increase (decrease) for actual return (loss) on plan assets still held	(7)	2
Pension | Mortgage backed and asset backed | Level 3 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets Level 3 reconciliation, increase (decrease) for actual return (loss) on plan assets still held	1	6
Pension | Other | Level 3 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets Level 3 reconciliation, increase (decrease) for actual return (loss) on plan assets still held		3
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 183	$ 163	$ 140
Other Postretirement Benefits | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	40.00%
Other Postretirement Benefits | Equity securities:
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	60.00%