CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ (37)	$ 33	$ (21)	$ 154	$ (125)	$ 204	$ 87	$ 164	$ 129	$ 330	$ 354
Net change in unrealized gains (losses), net of tax:
Investment securities									(227)	(392)	176
Other-than-temporarily impaired debt securities held-to-maturity									0	0	60
Derivatives designated as cash flow hedges									13	(14)	(73)
Pension and post-retirement benefit plans									3	0	(5)
Total other comprehensive income (loss)									(211)	(406)	158
Comprehensive income (loss)									$ (82)	$ (76)	$ 512