Stock Plans 8 (Details) - $ / shares shares in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Restricted Stock Awards (RSAs)
Summary of RSA and RSU activity under the Plans
Shares, Outstanding beginning balance	4.5	4.2	4.3
Weighted average grant date fair value, Outstanding beginning balance (in dollars per share)	$ 30.83	$ 29.51	$ 27.99
Shares, Granted	3.0	2.9	2.8
Weighted average grant date fair value, Granted (in dollars per share)	$ 31.76	$ 31.56	$ 30.59
Shares, Released	(2.3)	(2.1)	(2.1)
Weighted average grant date fair value, Released (in dollars per share)	$ 30.51	$ 29.27	$ 27.95
Shares, Forfeitures	(0.6)	(0.5)	(0.8)
Weighted average grant date fair value, Forfeitures (in dollars per share)	$ 31.41	$ 30.66	$ 29.44
Shares, Outstanding ending balance	4.6	4.5	4.2
Weighted average grant date fair value, Outstanding ending balance (in dollars per share)	$ 31.52	$ 30.83	$ 29.51
Restricted Stock Units (RSUs)
Summary of RSA and RSU activity under the Plans
Shares, Outstanding beginning balance	1.3	1.3	1.4
Weighted average grant date fair value, Outstanding beginning balance (in dollars per share)	$ 28.67	$ 27.35	$ 25.74
Shares, Granted	1.1	1.0	0.9
Weighted average grant date fair value, Granted (in dollars per share)	$ 30.47	$ 30.17	$ 28.72
Shares, Released	(1.0)	(0.9)	(0.8)
Weighted average grant date fair value, Released (in dollars per share)	$ 29.61	$ 28.51	$ 26.17
Shares, Forfeitures	(0.1)	(0.1)	(0.2)
Weighted average grant date fair value, Forfeitures (in dollars per share)	$ 29.31	$ 28.71	$ 26.88
Shares, Outstanding ending balance	1.3	1.3	1.3
Weighted average grant date fair value, Outstanding ending balance (in dollars per share)	$ 29.47	$ 28.67	$ 27.35