AOCI - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Income Before Income Taxes	$ 689	$ 550	$ 2,261	$ 2,179
Applicable income tax expense	140	114	483	442
Net income	549	436	1,778	1,737
ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net income	5	(5)	1	(14)
Net Unrealized Gains On Available For Sale Securities
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net losses (gains) included in net income	3	0	(3)	(9)
Income Before Income Taxes	3	0	3	(9)
Applicable income tax expense	(1)	0	(1)	2
Net income	2	0	2	(7)
Net Unrealized Gains On Available For Sale Securities | Net (Losses) Gains Included In Net Income
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net losses (gains) included in net income	3	0	3	(9)
Net Unrealized Gains On Cash Flow Hedge Activities
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	5	(2)	2	(2)
Income Before Income Taxes	5	(2)	2	(2)
Applicable income tax expense	(1)	0	0	0
Net income	4	(2)	2	(2)
Net Unrealized Gains On Cash Flow Hedge Activities | Interest Rate Contracts Related To C&I Loans
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	5	(2)	2	(2)
Amortization Of Defined Benefit Pension Items
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Income Before Income Taxes	(1)	(3)	(4)	(7)
Applicable income tax expense	0	0	1	2
Net income	(1)	(3)	(3)	(5)
Amortization Of Defined Benefit Pension Items | Net Actuarial Loss
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic pension cost	(1)	(1)	(4)	(5)
Amortization Of Defined Benefit Pension Items | Pension Settlement
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic pension cost	$ 0	$ (2)	$ 0	$ (2)