Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 376	$ 341	$ 1,005	$ 966
Noninterest income	681	650	1,850	1,808
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	115	105	328	313
Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	69	78	176	188
Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	77	86	229	251
Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	112	69	265	204
Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3	3	7	10
Noninterest income	274	278	747	752
Operating Segments | Consumer Bank
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	191	193	542	567
Operating Segments | Consumer Bank | Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	100	89	279	265
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	45	59	138	169
Operating Segments | Consumer Bank | Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	43	42	118	123
Operating Segments | Consumer Bank | Other noninterest income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3	3	7	10
Operating Segments | Commercial Bank
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	185	148	463	399
Operating Segments | Commercial Bank | Trust and investment services income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	15	16	49	48
Operating Segments | Commercial Bank | Investment banking and debt placement fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	69	78	176	188
Operating Segments | Commercial Bank | Services charges on deposit accounts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	32	27	91	82
Operating Segments | Commercial Bank | Cards and payments income
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	69	27	147	81
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	$ 31	$ 31	98	90
Segment Reconciling Items [Member]
Disaggregation of Revenue [Line Items]
Noninterest income			$ 1,850	$ 1,808