Investment Securities (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, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment Securities [Abstract]
Balance at beginning of period	$ 1	$ 2	$ 169
Credit losses recognized into current period earnings on debt securities for which an OTTI was not previously recognized			1
Reductions due to sale of debt securities for which an OTTI was previously recognized	$ (1)	(1)	(168)
Balance at end of period		$ 1	$ 2