AOCI (Reclassification Out of Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost		$ 9	$ 16	$ 13
Income Before Income Taxes		2,771	2,065	2,365
Applicable income tax expense		577	505	659
Net income		2,194	1,564	1,712
Total reclassifications for the period
Reclassifications Out Of Accumulated Other Comprehensive Income
Net income		1	26	48
Net unrealized gains on available-for-sale securities
Reclassifications Out Of Accumulated Other Comprehensive Income
Income Before Income Taxes	[1]	(3)	11	16
Applicable income tax expense	[1]	(1)	(4)	(6)
Net income	[1]	(4)	7	10
Net unrealized gains on available-for-sale securities | Net losses included in net income
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net losses (gains) included in net income	[1]	(3)	11	16
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		19	48	75
Income Before Income Taxes	[1]	19	48	75
Applicable income tax expense	[1]	(7)	(17)	(26)
Net income	[1]	12	31	49
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]	19	48	75
Amortization of defined periodic benefit costs
Reclassifications Out Of Accumulated Other Comprehensive Income
Income Before Income Taxes	[1]	(11)	(18)	(17)
Applicable income tax expense	[1]	4	6	6
Net income	[1]	(7)	(12)	(11)
Amortization of defined periodic benefit costs | Net Actuarial Loss
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[1],[2]	(7)	(11)	(10)
Amortization of defined periodic benefit costs | Pension Settlement
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[1],[2]	$ (4)	$ (7)	$ (7)

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

[2] This AOCI component is included in the computation of net periodi c benefit cost. Refer to Note 21 f or information on the computation of net periodic benefit cost.