Employee Benefits - Narrative (Detail) $ in Millions			10 Months Ended	12 Months Ended
	Mar. 06, 2024 retiree	Feb. 29, 2024 USD ($) agreement	Mar. 31, 2025 employee	Dec. 31, 2024 USD ($) plan shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for all defined benefit pension plans				$ 7,900	$ 15,100
Defined benefit plan, number of pension authorization commitment agreements | agreement		2
Liability, defined benefit plan		$ 5,800
Defined benefit plan, benefit obligation, actuarial gain (loss) from assumptions used calculating benefit obligation, discount rate				$ 1,400	$ (503)	$ 7,000
Discount Rate					5.00%	5.20%	2.90%
Defined benefit plan, benefit obligation, actuarial gain (loss) from healthcare cost assumptions used calculating benefit obligation, discount rate					$ (534)
Weighted-average healthcare cost trend rate assumed for next year				8.80%	7.30%	6.60%
Defined benefit plan, reclassification adjustment from AOCI				$ 0	$ 252	$ 390
Defined benefit plan, period used to determine overall expected long term rate of return on assets assumption (in years)				10 years
Number of leveraged employee stock ownership plans (ESOP) | plan				4
Number of allocated shares of common stock in ESOP (in shares) | shares				39,000,000
Number of unallocated shares of common stock in ESOP (in shares) | shares				0
Total savings plan cost				$ 700	724	620
Severance liability charged to expense				1,494	531	319
Defined benefit plan, actuarial gain (loss), immediate recognition as component in net periodic benefit (cost) credit				657	(992)	1,700
Pension and benefit credits (charges) from actual return				(1,000)	(503)	206
Defined benefit plan, benefit obligation, actuarial gain (loss) from actuarial assumption adjustments					45	(5,500)
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Restructuring and related cost, number of positions eliminated | employee			4,800
Minimum
Defined Benefit Plan Disclosure [Line Items]
Selected bonds				$ 300
Minimum | Return Seeking Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets				53.00%
Minimum | Liability Hedging Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets				41.00%
Maximum | Return Seeking Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets				63.00%
Maximum | Liability Hedging Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets				51.00%
Maximum | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets				10.00%
Pension
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, number of retirees receiving benefit payments from pension plan | retiree	56,000
Annuity contracts transfer				$ 5,611	0
Defined benefit plan, benefit obligation, actuarial gain (loss) from assumptions used calculating benefit obligation, discount rate				$ 764	$ (288)	4,100
Discount Rate				5.80%	5.00%
Defined benefit plan, benefit obligation, actuarial gain (loss) from pension annuitization		$ 200		$ 200
Defined benefit plan, benefit obligation, actuarial gain (loss) from healthcare cost assumptions used calculating benefit obligation, discount rate					$ (534)
Company contributions				421	252
Defined benefit plan, actuarial gain (loss), immediate recognition as component in net periodic benefit (cost) credit				110	(266)	(1,505)
Pension | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Company contributions				365
Pension | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Company contributions				56
Health Care and Life
Defined Benefit Plan Disclosure [Line Items]
Annuity contracts transfer				0	0
Defined benefit plan, benefit obligation, actuarial gain (loss) from assumptions used calculating benefit obligation, discount rate				$ 656	$ (215)	2,900
Discount Rate				5.60%	5.00%
Company contributions				$ 935	$ 936
Defined benefit plan contributions by employer in next fiscal year				726
Defined benefit plan, actuarial gain (loss), immediate recognition as component in net periodic benefit (cost) credit				$ 547	$ (726)	$ 3,182
Pension and Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate				5.70%