Deposits and Borrowings - Deposits and Short-term Borrowings (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Deposits:
Non-interest bearing deposits	$ 25,182	$ 25,847
Interest-bearing deposits	196,597	191,874
Total deposits	221,779	217,721	$ 210,440
Short-term Debt [Line Items]
Short-term borrowings	917	981
Federal funds purchased and securities loaned or sold under agreements to repurchase
Short-term Debt [Line Items]
Short-term borrowings	$ 917	$ 981