Fair Value Measurements Fair Value Measurements (Schedule of Cash and Cash Equivalents and Investments) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Cash and cash equivalents, at Carrying Value	$ 660	$ 1,118	$ 1,825	$ 1,391
Short-term Investments	1,539	1,441
Long-term Investments	187	420
Cash, Cash Equivalents, and Short-term Investments	2,386	2,979
Cash and Cash Equivalents [Member]
Schedule of Held-to-maturity Securities [Line Items]
Cash and cash equivalents, at Carrying Value	560	873
Short-term Investments	0	0
Long-term Investments	0	0
Cash, Cash Equivalents, and Short-term Investments	560	873
Commercial Paper [Member]
Schedule of Held-to-maturity Securities [Line Items]
Cash and cash equivalents, at Carrying Value	0	45
Short-term Investments	138	368
Long-term Investments	0	0
Cash, Cash Equivalents, and Short-term Investments	138	413
Corporate Bond Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Cash and cash equivalents, at Carrying Value	0	0
Short-term Investments	865	691
Long-term Investments	187	420
Cash, Cash Equivalents, and Short-term Investments	1,052	1,111
Bank Time Deposits [Member]
Schedule of Held-to-maturity Securities [Line Items]
Cash and cash equivalents, at Carrying Value	100	200
Short-term Investments	536	382
Long-term Investments	0	0
Cash, Cash Equivalents, and Short-term Investments	$ 636	$ 582