Debt Notes and Debentures (Details) - USD ($) $ in Millions	Dec. 31, 2016	May 31, 2016	Aug. 31, 2015	Mar. 31, 2015	Aug. 31, 2014	Mar. 31, 2014
Corporate Debt Securities | Three Point Nine Zero Zero Percent Debentures Due August 1, 2046 [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount		$ 750
Debt instrument interest rate		3.90%
Corporate Debt Securities | Three Point Six Five Zero Percent Debentures Due September 1, 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount			$ 350
Debt instrument interest rate			3.65%
Corporate Debt Securities | Four Point Seven Zero Zero Percent Debentures Due September 1, 2045 [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount			$ 650
Debt instrument interest rate			4.70%
Corporate Debt Securities | Three Point Zero Zero Zero Percent Debentures Due April 1, 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount				$ 500
Debt instrument interest rate				3.00%
Corporate Debt Securities | Four Point One Five Zero Percent Debentures Due April 1, 2045 [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount				$ 1,000
Debt instrument interest rate				4.15%
Corporate Debt Securities | Three Point Four Zero Zero Percent Debentures Due September 1, 2024 [Member] [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount					$ 700
Debt instrument interest rate					3.40%
Corporate Debt Securities | Four Point Five Five Zero Percent Debentures Due September 1, 2044 [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount					$ 800
Debt instrument interest rate					4.55%
Corporate Debt Securities | Three Point Seven Five Zero Percent Debentures Due April 1, 2024 [Member] [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount						$ 500
Debt instrument interest rate						3.75%
Corporate Debt Securities | Four Point Nine Zero Zero Percent Debentures Due April 1, 2044 [Member] [Member]
Debt Instrument [Line Items]
Debt Instrument issued amount						$ 1,000
Debt instrument interest rate						4.90%
SEC Debt Shelf Registration
Debt Instrument [Line Items]
Remaining amount of debt securities that may be issued	$ 1,500