Segments - Results of Operations and Average Assets by Segment (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Bank premises impairment	$ 2	$ 33	$ 22	$ 41
Other asset impairment charges			(1)	2
Bank premises and equipment held for sale	70		70		$ 42
Commercial Banking | Operating lease equipment
Segment Reporting Information [Line Items]
Other asset impairment charges				2
General Corporate and Other
Segment Reporting Information [Line Items]
Bank premises and equipment held for sale	$ 70	$ 37	$ 70	$ 37