Debt 2 (Details) (USD $)	6 Months Ended				1 Months Ended	6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Aug. 31, 2013 2.875% Senior Notes due August 2018 (2.875% Notes) [Member]	Aug. 31, 2013 4.500% Senior Notes due August 2023 (4.500% Notes) [Member]	Aug. 31, 2013 2.875% Notes and 4.500% Notes [Member]	Sep. 30, 2013 Revolving Credit Facility due June 2018 [Member]	Mar. 31, 2013 Revolving Credit Facility due August 2016 [Member]	Sep. 30, 2013 Base Rate Borrowings [Member]	Sep. 30, 2013 Eurocurrency Rate Borrowings [Member]
Debt (Textual) [Abstract]
Senior Notes, Face amount			$ 250,000,000	$ 250,000,000
Senior Notes, Interest rate			2.875%	4.50%
Proceeds from issuance of Senior Notes	498,000,000	0			498,000,000
Senior Notes, Discount					2,000,000
Additional basis points for redemption of Senior Notes			0.25%	0.30%
Debt issuance costs	4,000,000	0			4,000,000	1,000,000
Maximum committed amount available under revolving credit facility						1,000,000,000
Maximum available credit increase under revolving credit facility						500,000,000
Borrowings outstanding under revolving credit facility						$ 0	$ 0
Interest rate that would have applled at September 30, 2013 to a borrowing under revolving credit facility due June 2018								3.38%	1.18%
Covenant description						The revolving credit facility due June 2018 contains customary covenants for borrowings of this type, including two financial covenants: (i) for the 12 months ending each quarter-end, the ratio of consolidated debt for borrowed money to consolidated cash flow, each as defined in the Credit Agreement, must not exceed 4.00 to 1.00; and (ii) for the 12 months ending at any date, the ratio of consolidated cash flow to the sum of interest payable on, and amortization of debt discount in respect of, all consolidated debt for borrowed money, as defined in the Credit Agreement, must not be less than 3.50 to 1.00.
Financial covenant ratio of consolidated debt to consolidated cash flow						400.00%
Financial covenant ratio of consolidated cash flow to sum of interest payable and amortization of debt discount						350.00%
Covenant compliance						At September 30, 2013, the Company was in compliance with all covenants.