Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 65	$ 63	$ 86	$ 105
Total loans	88,222		88,222		$ 86,405
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Forgiveness of principal	5	0	5	0
Bankruptcy Plan Modification	7	29	7	29
Total	46	55	47	81
Total loans					62,733
Financing Receivable Modifications Concessions Extension Of Maturity Date	14	15	15	17
Financing Receivable Modifications Concessions Payment For Covenant Modification	20	11	20	35
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	10	4	18	7
Forgiveness of principal	0	0	0	0
Other	9	4	21	17
Total	19	$ 8	39	$ 24
Total loans					$ 23,672
Commercial Loans [Member] | Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Total loans	64,976		64,976
Consumer Portfolio Segment [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Total loans	$ 23,246		$ 23,246