Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of AOCI) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss				$ (4)
Pretax total		$ (51)	$ 5	(62)	$ 14
Unrealized Gains (Losses) on Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized (losses) gains on sales of debt securities		(50)	7	(58)	18
Tax effect		13	(2)	15	(4)
Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss	[1]	(1)	(2)	(4)	(5)
Amortization of prior service credit	[1]	0	0	0	1
Pretax total	[1]	(1)	(2)	(4)	(4)
Tax effect	[1]	$ 0	$ 1	$ 0	$ 1

[1] Amounts are components of net periodic cost. See Note 11 Employee Benefit Plans for additional details.