Quarterly Results (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Quarterly Results
Total revenue	$ 564.7	$ 548.2	$ 556.7	$ 502.4	$ 562.2	$ 539.9		$ 502.3	$ 460.9	$ 2,172.0	$ 2,065.3	$ 1,911.2
Gross Profit	404.9	410.6	414.7	372.9	428.5	409.0		391.6	352.6
Operating income	106.0	161.8	161.0	115.1	141.8	139.4	[1]	143.5	108.1	543.9	532.8	506.1
Net earnings	$ 70.7	$ 119.9	$ 114.7	$ 95.7	$ 122.5	$ 109.1		$ 131.8	$ 92.8	$ 401.0	$ 456.2	$ 406.1
Basic earnings per share	$ 0.43	$ 0.72	$ 0.66	$ 0.54	$ 0.69	$ 0.61		$ 0.74	$ 0.51	$ 2.36	$ 2.55	$ 2.21
Diluted earnings per share	$ 0.43	$ 0.71	$ 0.65	$ 0.53	$ 0.67	$ 0.60		$ 0.73	$ 0.50	$ 2.32	$ 2.50	$ 2.17
Shares used in computing basic earnings per share	163.3	167.2	173.0	176.3	178.1	178.2		178.3	180.3	169.9	178.7	183.1
Shares used in computing diluted earnings per share	165.6	169.5	176.0	180.6	182.3	182.3		181.4	183.8	172.8	182.4	186.8

[1] The unrealized losses on available-for-sale securities at March 31, 2012 and 2011 relate to the auction rate securities.