Share-Based Compensation (Details 1) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011 Y	Mar. 31, 2010
Summary of share-based compensation activity
Beginning Balance, Shares	7.2
Beginning Balance, Weighted-Average Exercise Price	$ 30
Beginning Balance, Weighted-Average Remaining Contractual Term	3
Beginning Balance, Aggregate Intrinsic Value	$ 144.9
Granted, Shares			0.2
Granted, Weighted-Average Exercise Price
Exercised, Shares	(1.5)
Exercised, Weighted-Average Exercise Price	$ 26
Cancelled or expired, Shares	(0.2)
Cancelled or expired, Weighted-Average Exercise Price	$ 34
Ending Balance, Shares	5.5	7.2
Ending Balance, Weighted-Average Exercise Price	$ 30	$ 30
Ending Balance, Weighted-Average Remaining Contractual Term	2	3
Ending Balance, Aggregate Intrinsic Value	57.1	144.9
Vested and expected to vest, Shares	5.5
Vested and expected to vest, Weighted-Average Exercise Price	$ 30
Vested and expected to vest, Weighted-Average Remaining Contractual Term	2
Vested and expected to vest, Aggregate Intrinsic Value	57.0
Exercisable, Shares	5.3
Exercisable, Weighted-Average Exercise Price	$ 30
Exercisable, Weighted-Average Remaining Contractual Term	2
Exercisable, Aggregate Intrinsic Value	$ 55.9