Stock-Based Compensation (Summary of Stock Option Activity) (Details) (Stock Option [Member], USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at the beginning of period, Number Of Stock Options	6,584,482	6,885,586	6,707,018
Granted, Number Of Stock Options	966,300	995,038	1,047,300
Exercised, Number Of Stock Options	(2,423,265)	(1,253,672)	(812,304)
Forfeited, Number Of Stock Options	(75,501)	(42,470)	(56,428)
Outstanding at the end of period, Number Of Stock Options	5,052,016	6,584,482	6,885,586
Vested or expected to vest as of March 31, 2013, Number Of Stock Options	5,037,557
Exercisable as of March 31, 2013, Number Of Stock Options	2,706,666
Outstanding at the beginning of period, Weighted-Average Exercise Price Per Share	$ 47.08	$ 41.11	$ 36.15
Granted, Weighted-Average Exercise Price Per Share	$ 91.52	$ 66.39	$ 62.56
Exercised, Weighted-Average Exercise Price Per Share	$ 36.67	$ 29.27	$ 27.20
Forfeited, Weighted-Average Exercise Price Per Share	$ 67.86	$ 57.35	$ 50.38
Outstanding at the end of period, Weighted-Average Exercise Price Per Share	$ 60.26	$ 47.08	$ 41.11
Vested or expected to vest as of March 31, 2013, Weighted-Average Exercise Price Per Share	$ 60.19
Exercisable at March 31, 2013, Weighted-Average Exercise Price Per Share	$ 49.79
Outstanding at the end of period, Aggregate Intrinsic Value	$ 196,527	$ 275,849	$ 174,350
Vested or expected to vest as of March 31, 2013, Aggregate Intrinsic Value	196,306
Exercisable as of March 31, 2013, Aggregate Intrinsic Value	$ 133,633