Securities Available for Sale and Securities Held to Maturity (Proceeds and Gross Realized Gains and Losses from Sales of Securities Available for Sale) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Securities Available for Sale and Securities Held to Maturity [Abstract]
Proceeds	$ 150	$ 1,285
Gross realized gains		$ 1