Employee Benefits - Reconciliation of Beginning and Ending Balance of Pension Plan Assets Measured at Fair Value (Detail) - Pension - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	$ 20,128	$ 19,451
End of year	20,087	20,128
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	1,507	1,850
Actual gain (loss) on plan assets	(45)	204
Purchases (sales)	421	(188)
Transfers out	(232)	(359)
End of year	1,651	1,507
Level 3 | Equity securities
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	2	3
Actual gain (loss) on plan assets	(1)	5
Purchases (sales)	(1)	(7)
Transfers out	0	1
End of year	0	2
Level 3 | Corporate bonds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	176	145
Actual gain (loss) on plan assets	(5)	(8)
Purchases (sales)	1	39
Transfers out	(172)	0
End of year	0	176
Level 3 | International bonds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	20	26
Actual gain (loss) on plan assets	0	3
Purchases (sales)	(4)	(9)
Transfers out	(16)	0
End of year	0	20
Level 3 | Real estate
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	757	810
Actual gain (loss) on plan assets	(21)	146
Purchases (sales)	197	(146)
Transfers out	39	(53)
End of year	972	757
Level 3 | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	414	737
Actual gain (loss) on plan assets	(19)	57
Purchases (sales)	147	(134)
Transfers out	27	(246)
End of year	569	414
Level 3 | Hedge funds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning of year	138	129
Actual gain (loss) on plan assets	1	1
Purchases (sales)	81	69
Transfers out	(110)	(61)
End of year	$ 110	$ 138