Business Segments and Revenue from Contracts with Customers - Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Total contract revenue	$ 1,468	$ 1,416	$ 2,858	$ 2,694
Revenue from other sources	492	483	1,016	922
Total non-interest income	1,960	1,899	3,874	3,616
Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	1,199	1,202	2,340	2,282
Revenue from other sources	307	297	642	580
Total non-interest income	1,506	1,499	2,982	2,862
Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	167	141	313	267
Revenue from other sources	5	8	18	17
Total non-interest income	172	149	331	284
Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	102	73	205	145
Revenue from other sources	169	184	347	324
Total non-interest income	271	257	552	469
Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0	0	0
Revenue from other sources	11	(6)	9	1
Total non-interest income	11	(6)	9	1
Interchange fees, net
Disaggregation of Revenue [Line Items]
Total contract revenue	1,249	1,213	2,394	2,352
Interchange fees, net | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	1,116	1,111	2,136	2,136
Interchange fees, net | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	107	92	205	178
Interchange fees, net | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	26	10	53	37
Interchange fees, net | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0	0	1
Service charges and other customer-related fees
Disaggregation of Revenue [Line Items]
Total contract revenue	96	77	190	137
Service charges and other customer-related fees | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0	0	0
Service charges and other customer-related fees | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	22	22	43	43
Service charges and other customer-related fees | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	74	55	147	95
Service charges and other customer-related fees | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0	0	(1)
Other
Disaggregation of Revenue [Line Items]
Total contract revenue	123	126	274	205
Other | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	83	91	204	146
Other | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	38	27	65	46
Other | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	2	8	5	13
Other | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	$ 0	$ 0	$ 0	$ 0