Stockholders' Equity (Schedule of Accumulated Other Comprehensive Income) (Details) $ in Millions	3 Months Ended
	Jun. 30, 2017 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
March 31, 2017	$ 3,487	[1]
June 30, 2017	3,389
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
March 31, 2017	7
Other comprehensive loss before reclassifications	(2)
June 30, 2017	5
Unrealized Gain on Available-For-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
March 31, 2017	5
Other comprehensive loss before reclassifications	0
June 30, 2017	5
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
March 31, 2017	12
Other comprehensive loss before reclassifications	(2)
June 30, 2017	$ 10

[1] Derived from audited financial statements.