AOCI (Reclassification Out of Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost		$ 8	$ 5	$ 9
Income (Loss) Before Income Taxes		3,202	2,765	2,979
Applicable income tax expense		690	572	799
Net income		2,512	2,193	2,180
Total reclassifications for the period
Reclassifications Out Of Accumulated Other Comprehensive Income
Net income		12	(18)	1
Net unrealized gains on available-for-sale securities
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net losses (gains) included in net income		9	(11)	(3)
Income (Loss) Before Income Taxes	[1]	9	(11)	(3)
Applicable income tax expense	[1]	(2)	2	(1)
Net income	[1]	7	(9)	(4)
Net unrealized gains on available-for-sale securities | Net gains (losses) included in net income
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net losses (gains) included in net income	[1]	9	(11)	(3)
Net unrealized gains on cash flow hedge derivatives
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		16	(2)	19
Income (Loss) Before Income Taxes	[1]	16	(2)	19
Applicable income tax expense	[1]	(3)	0	(7)
Net income	[1]	13	(2)	12
Net unrealized gains on cash flow hedge derivatives | Interest rate contracts related to C&I loans
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	[1]	16	(2)	19
Amortization of defined periodic benefit costs
Reclassifications Out Of Accumulated Other Comprehensive Income
Income (Loss) Before Income Taxes	[1]	(9)	(9)	(11)
Applicable income tax expense	[1]	1	2	4
Net income	[1]	(8)	(7)	(7)
Amortization of defined periodic benefit costs | Net Actuarial Loss
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[2]	(6)	(6)	(7)
Amortization of defined periodic benefit costs | Pension Settlement
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[2]	$ (3)	$ (3)	$ (4)

[1] Amounts in parentheses indicate reductions to net income.

[2] This AOCI component is included in the computation of net periodic benefit cost. Refer to Note 23 for information on the computation of net periodic benefit cost.