Stock-Based Compensation Plans (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012 Y
Summary of options Outstanding
Vested (Exercisable), Number of Shares	15,349
Vested (Exercisable), Weighted Average Exercise Price Per Share	$ 28.78
Vested (Exercisable), Weighted Average Remaining Contractual Term	2.84
Vested (Exercisable), Aggregate Intrinsic Value	$ 133,990
Expected to Vest, Number of Shares	2,323
Expected to Vest, Weighted Average Exercise Price Per Share	$ 25.51
Expected to Vest, Weighted Average Remaining Contractual Term	5.12
Expected to Vest, Aggregate Intrinsic Value	25,474
Vested and Expected to Vest, Number of Shares	17,672
Vested and Expected to Vest, Weighted Average Exercise Price	$ 28.35
Vested and Expected to Vest, Weighted Average Remaining Contractual Term	3.14
Vested and Expected to Vest, Aggregate Intrinsic Value	159,464
Vested and Expected to Vest Outstanding, Number of Shares	17,788
Vested and Expected to Vest Outstanding, Weighted Average Exercise Price	$ 28.32
Vested and Expected to Vest Outstanding, Weighted Average Remaining Contractual Term	3.14
Vested and Expected to Vest Outstanding, Aggregate Intrinsic Value	$ 160,941