Equity Incentive Plans, Stock Options Outstanding (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Summary of information about stock options outstanding [Line Items]
Aggregate intrinsic value of options exercisable related to stock incentive plans	$ 41.0
Closing price of company's common stock related to calculation of aggregate intrinsic value of stock options (in dollars per share)	$ 37.20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Option shares outstanding beginning balance (in shares)	5,496,924	8,459,779	10,081,533
Options granted (in shares)	0	0	12,000
Options exercised (shares)	(2,129,260)	(2,885,365)	(1,492,866)
Options canceled (in shares)	(6,667)	(77,490)	(140,888)
Option shares outstanding ending balance (in shares)	3,360,997	5,496,924	8,459,779
Option shares outstanding beginning balance (in dollars per share)	$ 25.21	$ 24.52	$ 24.20
Options granted (in dollars per shares)	$ 0.00	$ 0.00	$ 27.03
Options exercised (in dollars per share)	$ 25.53	$ 23.09	$ 22.03
Options canceled (in dollars per share)	$ 25.05	$ 29.39	$ 27.79
Option shares outstanding ending balance (in dollars per share)	$ 25.00	$ 25.21	$ 24.52
Stock Option [Member]
Summary of information about stock options outstanding [Line Items]
Total intrinsic value of options exercised related to stock incentive plans	26.7	29.8	7.6
Aggregate intrinsic value of options outstanding related to stock incentive plans	$ 41.0
Exercisable number of option shares (in shares)	3,360,997,000	5,491,363,000
Weighted average exercise price per share of exercisable options (in dollars per share)	$ 25.00	$ 25.20
Weighted average fair value per share of stock options granted			$ 5.90
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected term			6.50
Volatility			36.00%
Risk free interest rate			3.00%
Dividend yield			5.00%