Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 436	$ 321	$ 817	$ 629
Noninterest income	750	692	1,488	1,169
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	120	102	240	213
Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	121	60	202	107
Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	82	68	156	152
Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	111	89	214	153
Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	2	5	4
Noninterest income	273	346	595	484
Operating Segments | Consumer Bank
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	202	164	386	352
Operating Segments | Consumer Bank | Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	105	87	206	179
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	48	38	88	94
Operating Segments | Consumer Bank | Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	47	37	88	75
Operating Segments | Consumer Bank | Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	2	4	4
Operating Segments | Commercial Bank
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	234	157	431	277
Operating Segments | Commercial Bank | Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	15	15	34	34
Operating Segments | Commercial Bank | Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	121	60	202	107
Operating Segments | Commercial Bank | Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	34	30	68	58
Operating Segments | Commercial Bank | Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	64	52	126	78
Operating Segments | Commercial Bank | Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	1	0
Other
Disaggregation of Revenue [Line Items]
Noninterest income	$ 41	$ 25	$ 76	$ 56