Debt and Financing Activities - Revolving Credit Facilities (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Mar. 31, 2013 USD ($)	Mar. 31, 2012 USD ($)	Oct. 31, 2015 USD ($)	Mar. 31, 2015 EUR (€)
Global Facility
Line of Credit Facility [Line Items]
Credit facility borrowing capacity	$ 3,500,000,000.0						$ 3,500,000,000.0
Revolving credit facility term	5 years
Aggregate sublimit	$ 3,150,000,000
Credit facility outstanding, long-term		$ 0
Debt to capital ratio		0.65
Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility borrowing capacity							$ 1,300,000,000.0	€ 500,000,000
Revolving credit facility term			5 years
Amount borrowed under facility			$ 0	$ 0	$ 0	$ 0
Line of Credit
Line of Credit Facility [Line Items]
Credit facility borrowing capacity		$ 427,000,000
Bilateral Lines of Credit
Line of Credit Facility [Line Items]
Amount borrowed under facility		$ 641,000,000	225,000,000
Interest rate, minimum		0.18%
Interest rate, maximum		6.00%
Repayments of lines of credit		$ 635,000,000	267,000,000
Outstanding amount under credit lines		$ 28,000,000	$ 29,000,000