Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 321	$ 333	$ 629	$ 625
Noninterest income	692	622	1,169	1,158
Contract assets	0	0	0	0
Contract liabilities	0	0	0	0
Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	102	109	213	208
Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	60	65	107	110
Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	68	83	152	166
Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	89	72	153	135
Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	4	4	6
Noninterest income	331	253	473	474
Operating Segments | Consumer Bank
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	164	196	352	374
Operating Segments | Consumer Bank | Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	87	92	179	176
Operating Segments | Consumer Bank | Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Consumer Bank | Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	38	56	94	111
Operating Segments | Consumer Bank | Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	37	44	75	81
Operating Segments | Consumer Bank | Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	4	4	6
Operating Segments | Commercial Bank
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	157	137	277	251
Operating Segments | Commercial Bank | Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	15	17	34	32
Operating Segments | Commercial Bank | Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	60	65	107	110
Operating Segments | Commercial Bank | Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	30	27	58	55
Operating Segments | Commercial Bank | Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	52	28	78	54
Operating Segments | Commercial Bank | Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Noninterest income	$ 40	$ 36	67	59
Segment Reconciling Items [Member]
Disaggregation of Revenue [Line Items]
Noninterest income			$ 1,169	$ 1,158