Securities Available for Sale and Securities Held to Maturity (Rollforward Amount of Credit Losses Recognized in Earnings for OTTI Securities for Portion of Impairment Recognized in or Reclassified From Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Securities Available for Sale and Securities Held to Maturity [Abstract]
Balance at beginning of period	$ 2	$ 169	$ 159
Credit losses recognized into current period earnings on debt securities for which an OTTI was not previously recognized		1	1
Credit losses recognized into current period earnings on debt securities for which an OTTI was previously recognized			9
Reductions due to sale of debt securities for which an OTTI was previously recognized	(1)	(168)
Balance at end of period	$ 1	$ 2	$ 169