Short-Term Borrowings-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
Federal funds purchased (day to day) [Member]
Short-term Debt [Line Items]
Short-term borrowings	0					700					0		700
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 during year	8,902		9,106	16,849	19,300	14,781		11,371	8,794	7,538	13,498		10,643
Maximum month-end balance											19,254		18,748
Interest rate at the end of the period	0.48%	[1]				0.15%	[1]				0.48%	[1]	0.15%	[1]
Interest rate average during year	0.26%					0.24%					0.26%		0.24%
Commercial paper [Member]
Short-term Debt [Line Items]
Short-term borrowings	4,772					3,379					4,772		3,379
Average during year											4,537		3,969
Maximum month-end balance											4,963		4,990
Interest rate at the end of the period	0.23%					0.22%					0.23%		0.22%
Interest rate average during year	0.23%					0.25%					0.23%		0.25%
Precious metals [Member]
Short-term Debt [Line Items]
Short-term borrowings	40					1,517					40		1,517
Other [Member]
Short-term Debt [Line Items]
Short-term borrowings	$ 276					$ 618					$ 276		$ 618

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