Equity Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			$ 6,071
Net other comprehensive income (loss)	$ 25	$ (207)	(52)	$ (484)
Ending balance	3,648		3,648
Accumulated net unrealized investment gain (loss), AFS securities [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	643	1,085	716	1,358
Other comprehensive income (loss) before reclassifications	47	33	67	(6)
Amounts reclassified from other comprehensive income (loss)	(20)	(238)	(113)	(472)
Net other comprehensive income (loss)	27	(205)	(46)	(478)
Ending balance	670	880	670	880
Accumulated other comprehensive income (loss), Other [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	39	45	43	49
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from other comprehensive income (loss)	(2)	(2)	(6)	(6)
Net other comprehensive income (loss)	(2)	(2)	(6)	(6)
Ending balance	37	43	37	43
Accumulated other comprehensive income [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	682	1,130	759	1,407
Other comprehensive income (loss) before reclassifications	47	33	67	(6)
Amounts reclassified from other comprehensive income (loss)	(22)	(240)	(119)	(478)
Net other comprehensive income (loss)	25	(207)	(52)	(484)
Ending balance	$ 707	$ 923	$ 707	$ 923