CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (125)	$ 204	$ 87	$ 164	$ 70	$ 1	$ 179	$ 104	$ 330	$ 354	$ (338)
Net change in unrealized gains (losses), net of tax:
Investment securities									(392)	176	(1,010)
Other-than-temporarily impaired debt securities held-to-maturity									0	60	7
Derivatives designated as cash flow hedges									(14)	(73)	118
Pension and post-retirement benefit plans									0	(5)	8
Total other comprehensive income (loss)									(406)	158	(877)
Comprehensive income (loss)									$ (76)	$ 512	$ (1,215)