Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment securities:
Interest-bearing deposits with banks	$ 416	$ 387	$ 180
U.S. Treasury and federal agencies	1,443	1,178	854
State and political subdivisions	49	143	226
Other investments	505	560	658
Securities purchased under resale agreements	364	335	264
Loans and leases	769	687	504
Other interest-earning assets	395	372	222
Total interest income	3,941	3,662	2,908
Interest expense:
Interest-bearing deposits	663	363	163
Securities sold under repurchase agreements	31	13	2
Other short-term borrowings	21	17	10
Long-term debt	414	389	308
Other interest-bearing liabilities	246	209	121
Total interest expense	1,375	991	604
Net interest income	$ 2,566	$ 2,671	$ 2,304