Fair Value Measurements and Investments Carrying amount and estimated fair value of debt (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Debt Instrument [Line Items]
Carrying Amount	$ 15,882		$ 0
Senior Notes
Debt Instrument [Line Items]
Carrying Amount	15,882	$ 15,900
Estimated Fair Value	17,158
2017 Notes | Senior Notes
Debt Instrument [Line Items]
Carrying Amount	1,746
Estimated Fair Value	1,754
2020 Notes | Senior Notes
Debt Instrument [Line Items]
Carrying Amount	2,988
Estimated Fair Value	3,077
2022 Notes | Senior Notes
Debt Instrument [Line Items]
Carrying Amount	2,238
Estimated Fair Value	2,359
2025 Notes | Senior Notes
Debt Instrument [Line Items]
Carrying Amount	3,964
Estimated Fair Value	4,225
2035 Notes | Senior Notes
Debt Instrument [Line Items]
Carrying Amount	1,485
Estimated Fair Value	1,698
2045 Notes | Senior Notes
Debt Instrument [Line Items]
Carrying Amount	3,461
Estimated Fair Value	$ 4,045