Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Jun. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	$ 17,718.9	$ 16,927.5
Percent of Level Two Investment Pricing Inputs Provided by Pricing Service	99.00%
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	22.9	20.1
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	17,696.0	16,907.4
Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	17,718.9	16,927.5
U.S. Treasury And Direct Obligations Of U.S. Government Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	6,683.6	6,759.1
U.S. Treasury And Direct Obligations Of U.S. Government Agencies [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	6,683.6	6,759.1
Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	7,142.9	6,126.6
Corporate Bonds [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	7,142.9	6,126.6
Asset-Backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	414.4	447.8
Asset-Backed Securities [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	414.4	447.8
Commercial Mortgage Backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	337.2	492.5
Commercial Mortgage Backed Securities [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	337.2	492.5
Municipal Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	539.3	516.2
Municipal Bonds [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	539.3	516.2
Canadian Government Obligations And Canadian Government Agency Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	1,043.3	1,101.5
Canadian Government Obligations And Canadian Government Agency Obligations [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	1,043.3	1,101.5
Other Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	22.9	20.1
Other Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	1,535.3	1,463.7
Other Securities [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	1,558.2	1,483.8
Corporate Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	124.8	134.3
Funds Held For Clients [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	$ 17,594.1	$ 16,793.2