Consolidated Statements Of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statements of Comprehensive Income (Loss)
Net income (loss)	$ (17)	$ (98)
Unrealized gains (losses) on available-for-sale securities: [Abstract]
Unrealized gains (losses) arising during the period	79	(43)
Provision (benefit) for income taxes	4	5
Total	75	(48)
Reclassification adjustments for (gains) losses included in net income (loss)	(39)	(1)
Provision (benefit) for income taxes	0	0
Total	(39)	(1)
Available-for-sale securities with other-than-temporary impairments: [Abstract]
Other-than-temporary impairments and unrealized gains (losses) arising during the period	11	6
Provision (benefit) for income taxes	0	0
Total	11	6
Reclassification adjustments for (gains) losses included in net income (loss)	28	1
Provision (benefit) for income taxes	0	0
Total	28	1
Foreign currency translation: [Abstract]
Foreign currency translation gains (losses)	1	1
Provision (benefit) for income taxes	0	0
Total	1	1
Reclassification adjustments for (gains) losses included in net income (loss)	0	0
Provision (benefit) for income taxes	0	0
Reclassification adjustments for (gains) losses included in net income (loss)	0	0
Instrument-specific credit risk of liabilities measured at fair value: [Abstract]
Net gains (losses) of financial instruments at fair value	2	(14)
Provision (benefit) for income taxes	0	0
Total	2	(14)
Reclassification adjustments for (gains) losses included in net income (loss)	4	0
Provision (benefit) for income taxes	0	0
Total	4	0
Total other comprehensive income (loss)	82	(55)
Comprehensive income (loss)	$ 65	$ (153)