Loans TDR Modifications (Details) $ in Millions		12 Months Ended
		Dec. 31, 2017 USD ($) contracts	[1]	Dec. 31, 2016 USD ($) contracts		Dec. 31, 2015 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		7,136		9,278	[2]	5,599	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 74		$ 93	[2]	$ 157	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		299		389	[2]	193	[3]
Financing Receivable, Amount Restructured During Period		$ 373		$ 482	[2]	$ 350	[3]
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		178		84	[2]	57	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 3		$ 2	[2]	$ 1	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		43		68	[2]	3	[3]
Financing Receivable, Amount Restructured During Period		$ 46		$ 70	[2]	$ 4	[3]
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts	[3]					2
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted	[3]					$ 0
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted	[3]					0
Financing Receivable, Amount Restructured During Period	[3]					$ 0
Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts				1	[2]	1	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted				$ 0	[2]	$ 0	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted				0	[2]	0	[3]
Financing Receivable, Amount Restructured During Period				$ 0	[2]	$ 0	[3]
Residential Nonguaranteed [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		150		397	[2]	737	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 22		$ 79	[2]	$ 125	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		10		12	[2]	34	[3]
Financing Receivable, Amount Restructured During Period		$ 32		$ 91	[2]	$ 159	[3]
Home Equity Line of Credit [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		2,488		2,611	[2]	1,888	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 45		$ 9	[2]	$ 24	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		176		227	[2]	108	[3]
Financing Receivable, Amount Restructured During Period		$ 221		$ 236	[2]	$ 132	[3]
Residential Construction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts				1	[2]	4	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted				$ 0	[2]	$ 5	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted				0	[2]	0	[3]
Financing Receivable, Amount Restructured During Period				$ 0	[2]	$ 5	[3]
Consumer Other Direct [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		661		3,925	[2],[4]	54	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 0		$ 0	[2],[4]	$ 0	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		9		50	[2],[4]	1	[3]
Financing Receivable, Amount Restructured During Period		$ 9		$ 50	[2],[4]	$ 1	[3]
Consumer Indirect [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		2,740		1,539	[2]	2,299	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 0		$ 0	[2]	$ 0	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		61		32	[2]	47	[3]
Financing Receivable, Amount Restructured During Period		$ 61		$ 32	[2]	$ 47	[3]
Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts		919		720	[2]	557	[3]
Financing Receivable, Amount Restructured During Period, Rate Modifications Granted		$ 4		$ 3	[2]	$ 2	[3]
Financing Receivable, Amount Restructured During Period, Term Extension and/or Other Concessions Granted		0		0	[2]	0	[3]
Financing Receivable, Amount Restructured During Period		$ 4		$ 3	[2]	$ 2	[3]
Loans Modified Prior to 2016 [Member] | Consumer Other Direct [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Restructured During Period, Number Of Contracts | contracts				3,321
Financing Receivable, Amount Restructured During Period				$ 41

[1] Includes loans modified under the terms of a TDR that were charged-off during the period.

[2] Includes loans modified under the terms of a TDR that were charged-off during the period.

[3] Includes loans modified under the terms of a TDR that were charged-off during the period.

[4] Includes 3,321 loans with a carrying value of $41 million that were modified prior to 2016 and reclassified as TDRs in the fourth quarter of 2016.