Fair Value Measurements (Carrying Value And Fair Value Of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	$ 2,007,148	$ 2,107,096
4.50% senior notes due September 2014 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	0	399,952
Long-term debt, fair value	0	407,092
3.25% senior notes due October 2015 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	249,925	249,887
Long-term debt, fair value	255,218	258,630
2.95% senior notes due June 2016 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	249,883	249,848
Long-term debt, fair value	257,440	259,257
1.65% senior notes due February 2018 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	324,634	324,579
Long-term debt, fair value	320,603	319,098
2.375% senior notes due February 2020 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	274,770	274,748
Long-term debt, fair value	270,421	265,600
2.90% senior notes due November 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	249,773	249,760
Long-term debt, fair value	240,295	233,230
3.65% senior notes due July 2024 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	299,432	0
Long-term debt, fair value	$ 300,459	$ 0