Securities Available for Sale and Securities Held to Maturity (Proceeds and Gross Realized Gains (Losses) from Sales of Securities Available for Sale) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Securities Available for Sale and Securities Held to Maturity [Abstract]
Proceeds	$ 3,004	$ 1,073	$ 3,004	$ 1,323
Gross realized gains	$ 3	$ 2	$ 3	$ 2