- Revenues and Expenses with Affiliates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Securities borrowed or purchased under resale agreements	$ 765	$ 652	$ 347
Interest Expense, Deposits	826	441	241
Commercial paper and other short-term borrowings	202	168	58
Long-term debt	497	365	250
Securities loaned or sold under repurchase agreements	830	734	353
Fees from affiliates	1,439	1,213	866
Other	204	250	252
Other Noninterest Expense	422	409	389
MUSA and Various other Non-Bank Subsidiaries | Affiliated Entity
Related Party Transaction [Line Items]
Securities borrowed or purchased under resale agreements	66	66	41
Interest Income, Other	2	2	1
Interest Expense, Deposits	13	3	5
Commercial paper and other short-term borrowings	3	2	15
Long-term debt	237	171	114
Securities loaned or sold under repurchase agreements	25	18	6
Fees from affiliates	1,439	1,213	866
Other	(6)	1	13
Other Noninterest Expense	$ 96	$ 115	$ 112