Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 130	$ 71	$ 83
Total loans	86,405	86,038
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	0	0	0
Forgiveness of principal	0	0	22
Extension of maturity date	12	0	21
Payment or covenant modification/deferment	46	19	0
Bankruptcy plan modification	31	18	0
Total	89	37	43
Total loans	62,733	61,909
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	13	10	19
Forgiveness of principal	0	3	4
Other	28	21	17
Total	41	34	$ 40
Total loans	$ 23,672	$ 24,129