- Revenues and Expenses with Affiliates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Securities borrowed or purchased under resale agreements	$ 195	$ 112	$ 68
Commercial paper and other short-term borrowings	32	13	59
Long-term debt	240	250	190
Securities loaned or sold under repurchase agreements	140	52	21
Fees from affiliates	957	763	320
Other	74	92	130
Other Noninterest Expense	479	465	503
MUSA and Various other Non-Bank Subsidiaries | Affiliated Entity
Related Party Transaction [Line Items]
Securities borrowed or purchased under resale agreements	26	22	12
Commercial paper and other short-term borrowings	24	21	51
Long-term debt	69	27	32
Securities loaned or sold under repurchase agreements	2	1	1
Fees from affiliates	957	763	320
Other	(28)	17	63
Other Noninterest Expense	$ 95	$ 92	$ 83