Investment Securities (Impairments) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2012
Pre-tax, Other-Than-Temporary Impairments on Investment Securities
Total pre tax, OTTI recognized	[1]	$ 2	$ 2	$ 21	$ 18
Less other-than-temporary impairment recognized in accumulated other comprehensive income	[1]	0	0	0	4
Net other-than-temporary impairments on investment securities	[1]	2	2	21	14
Other Than Temporary Impairment Related To Equity Securities					2	$ 0
Changes in Cumulative Credit Loss Impairments Recognized on Debt Securities
Cumulative credit loss impairments recognized, beginning of period		6	255
Credit loss impairments recognized on securities not previously impaired		0	0	0	0
Incremental credit loss impairments recognized on securities previously impaired		0	2	0	4
Less: credit loss impairments previously recognized on securities sold during the period		0	0	2	53
Cumulative credit loss impairments recognized, end of period		$ 6	$ 257	$ 6	$ 257

[1] Amounts may not add due to rounding.