Short-Term Borrowings-Quarterly Schedule (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012		Dec. 31, 2011
Short-term Debt [Line Items]
Quarter end balance	$ 14,933								$ 16,009								$ 14,933		$ 16,009
Securities sold under repurchase agreements [Member]
Short-term Debt [Line Items]
Quarter end balance	6,817	[1],[2]	3,238	[1],[2]	3,843	[1],[2]	4,813	[1],[2]	7,417	[1],[2]	12,913	[1],[2]	8,463	[1],[2]	8,807	[1],[2]	6,817	[1],[2]	7,417	[1],[2]
Average quarterly balance	$ 5,481		$ 5,155		$ 5,394		$ 8,168		$ 11,560		$ 10,913		$ 9,927		$ 13,949		$ 6,046		$ 11,579

[1] The following table presents the quarter end and average quarterly balances of securities sold under repurchase agreements: 2012 2011 Fourth Third Second First Fourth Third Second First (in millions)Quarter end balance$6,817 $3,238 $3,843 $4,813 $7,417 $12,913 $8,463 $8,807Average quarterly balance5,481 5,155 5,394 8,168 11,560 10,913 9,927 13,949

[2] Exceeded 30 percent of shareholders’ equity at December 31, 2012 and 2011.