Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 13	$ 21
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Extension of Maturity Date	0	1
Total	0	1
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	4	8
Other	9	12
Total	$ 13	$ 20