Debt and Financing Activities - Revolving Credit Facilities (Details)	9 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Oct. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)
Revolving Credit Facility
Line of Credit Facility [Line Items]
Syndicated senior unsecured revolving credit facility			€ 500,000,000	$ 1,300,000,000.0	$ 3,500,000,000.0
Syndicated senior unsecured revolving credit facility term	5 years
Borrowings under the facility	$ 0	$ 0
Amounts outstanding under facility				0		$ 0
Global Facility
Line of Credit Facility [Line Items]
Syndicated senior unsecured revolving credit facility				3,500,000,000.0
Credit facility, aggregate sublimit				$ 3,150,000,000
Debt to capital covenant ratio (no greater than)			0.65	0.65
Line of Credit
Line of Credit Facility [Line Items]
Syndicated senior unsecured revolving credit facility				$ 1,100,000,000
Borrowings under the facility	631,000,000	222,000,000
Amounts outstanding under facility				$ 29,000,000		$ 29,000,000
Repayments amount under credit lines	$ 633,000,000	$ 181,000,000
Line of Credit | Minimum
Line of Credit Facility [Line Items]
Credit lines interest rate	0.18%
Line of Credit | Maximum
Line of Credit Facility [Line Items]
Credit lines interest rate	6.00%