Consolidated Statements Of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statements of Comprehensive Income (Loss)
Net income (loss)	$ (1,605)	$ (338)	$ 180
Unrealized gains (losses) on available-for-sale securities: [Abstract]
Unrealized gains (losses) arising during the period	(22)	28	(80)
Provision (benefit) for income taxes	(1)	7	(27)
Total	(21)	21	(53)
Reclassification adjustments for (gains) losses included in net income (loss)	2	(1)	(7)
Provision (benefit) for income taxes	0	1	(3)
Total	2	(2)	(4)
Available-for-sale securities with other-than-temporary impairments: [Abstract]
Other-than-temporary impairments and unrealized gains (losses) arising during the period	(3)	10	(3)
Provision (benefit) for income taxes	0	4	(1)
Total	(3)	6	(2)
Reclassification adjustments for (gains) losses included in net income (loss)	7	4	4
Provision (benefit) for income taxes	1	1	1
Total	6	3	3
Foreign currency translation: [Abstract]
Foreign currency translation gains (losses)	146	(94)	(40)
Provision (benefit) for income taxes	21	1	(14)
Total	125	(95)	(26)
Total other comprehensive income (loss)	109	(67)	(82)
Comprehensive income (loss)	$ (1,496)	$ (405)	$ 98