Equity Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			$ 6,071
Net other comprehensive income (loss)	$ (83)	$ (77)	(77)	$ (277)
Ending balance	3,717		3,717
Accumulated net unrealized investment gain (loss), AFS securities [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	724	1,160	716	1,358
Other comprehensive income (loss) before reclassifications	11	50	20	(39)
Amounts reclassified from other comprehensive income (loss)	(92)	(125)	(93)	(234)
Net other comprehensive income (loss)	(81)	(75)	(73)	(273)
Ending balance	643	1,085	643	1,085
Accumulated other comprehensive income (loss), Other [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	41	47	43	49
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from other comprehensive income (loss)	(2)	(2)	(4)	(4)
Net other comprehensive income (loss)	(2)	(2)	(4)	(4)
Ending balance	39	45	39	45
Accumulated other comprehensive income [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	765	1,207	759	1,407
Other comprehensive income (loss) before reclassifications	11	50	20	(39)
Amounts reclassified from other comprehensive income (loss)	(94)	(127)	(97)	(238)
Net other comprehensive income (loss)	(83)	(77)	(77)	(277)
Ending balance	$ 682	$ 1,130	$ 682	$ 1,130