Stock Plans 4 (Details) - $ / shares shares in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Stock option activity
Number of shares, Outstanding beginning balance	3.8	3.7	3.2
Weighted average exercise price, Outstanding beginning balance (in dollars per share)	$ 28.88	$ 27.72	$ 27.02
Number of shares, Granted	1.0	1.1	0.8
Weighted average exercise price, Granted (in dollars per share)	$ 31.69	$ 31.84	$ 30.39
Number of shares, Exercised	(0.5)	(0.8)	(0.2)
Weighted average exercise price, Exercised (in dollars per share)	$ 29.36	$ 27.09	$ 25.58
Number of shares, Expired or terminated	0.0	(0.2)	(0.1)
Weighted average exercise price, Expired or terminated (in dollars per share)	$ 0.00	$ 30.82	$ 31.08
Number of shares, Outstanding ending balance	4.3	3.8	3.7
Weighted average exercise price, Outstanding ending balance (in dollars per share)	$ 29.48	$ 28.88	$ 27.72
Options exercisable
Number of shares, Options exercisable	2.4	2.1	2.0
Weighted average exercise price, Options exercisable (in dollars per share)	$ 27.79	$ 27.09	$ 26.16