Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of AOCI) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss		$ (2)
Unrealized Gains (Losses) on Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized (losses) gains on sales of debt securities		(1)	$ 5
Tax effect			(1)
Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss	[1]	(2)	(2)
Tax effect	[1]	$ 1	$ 1

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