Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of AOCI) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss				$ (3)
Pretax total		$ (8)	$ 6	(11)	$ 9
Unrealized Gains (Losses) on Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized (losses) gains on sales of debt securities		(7)	6	(8)	11
Tax effect		2	(2)	2	(3)
Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss	[1]	(1)	(1)	(3)	(3)
Amortization of prior service credit	[1]	0	1	0	1
Pretax total	[1]	(1)	0	(3)	(2)
Tax effect	[1]	$ 0	$ 0	$ 1	$ 0

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