Short-Term Borrowings-Quarterly Schedule (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013
Short-term Debt [Line Items]
Short-term borrowings	$ 12,795					$ 19,135					$ 12,795		$ 19,135
Securities sold under repurchase agreements [Member]
Short-term Debt [Line Items]
Short-term borrowings	7,707	[1]	6,634	6,481	19,254	12,921	[1]	12,523	12,445	3,659	7,707	[1]	12,921	[1]
Average quarterly balance	$ 8,902		$ 9,106	$ 16,849	$ 19,300	$ 14,781		$ 11,371	$ 8,794	$ 7,538	$ 13,498		$ 10,643

[1] The following table presents the quarter end and average quarterly balances of securities sold under repurchase agreements: