Available-for-Sale Securities Summary of Available-for-Sale Securities at Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Available-for-Sale Securities
Amortized Cost	$ 23,218	$ 9,628
Gross Unrealized Gains	16	0
Gross Unrealized Losses	(14)	(3)
Estimated Fair Value	23,220	9,625
Money market funds
Available-for-Sale Securities
Amortized Cost	12,029	7,926
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	12,029	7,926
Corporate debt securities
Available-for-Sale Securities
Amortized Cost	4,832	941
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(13)	(3)
Estimated Fair Value	4,824	938
U.S. treasury securities
Available-for-Sale Securities
Amortized Cost	3,370	363
Gross Unrealized Gains	8	0
Gross Unrealized Losses	0	0
Estimated Fair Value	3,378	363
Residential mortgage and asset-backed securities
Available-for-Sale Securities
Amortized Cost	1,305	269
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(1)	0
Estimated Fair Value	1,306	269
Certificates of deposit
Available-for-Sale Securities
Amortized Cost	489	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	489	0
U.S. government agencies securities
Available-for-Sale Securities
Amortized Cost	863	113
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Estimated Fair Value	864	113
Non-U.S. government securities
Available-for-Sale Securities
Amortized Cost	301	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	301	0
Municipal debt securities
Available-for-Sale Securities
Amortized Cost	29	16
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 29	$ 16

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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