Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 60	$ 18	$ 124	$ 117
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Extension of Maturity Date	20	7	20	24
Payment or Covenant Modification/Deferment	26	0	46	32
Bankruptcy Plan Modification	0	0	7	30
Total	46	7	73	86
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	4	3	22	10
Other	10	8	29	21
Total	$ 14	$ 11	$ 51	$ 31