Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Banking and Thrift [Abstract]
Interest-bearing deposits with banks	$ 98	$ 94	$ 326	$ 267
U.S. Treasury and federal agencies	363	300	1,092	835
State and political subdivisions	12	29	37	125
Other investments	126	136	374	434
Securities purchased under resale agreements	101	87	289	246
Loans and leases	194	173	587	498
Other interest-earning assets	107	97	330	275
Total interest income	1,001	916	3,035	2,680
Interest-bearing deposits	173	84	553	236
Securities sold under repurchase agreements	7	4	27	11
Other short-term borrowings	8	4	18	12
Long-term debt	99	100	312	293
Other interest-bearing liabilities	70	52	195	154
Total interest expense	357	244	1,105	706
Net interest income	$ 644	$ 672	$ 1,930	$ 1,974