Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Jun. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	$ 18,417.0	$ 18,093.4
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	21.8	20.6
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	18,395.2	18,072.8
Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	18,417.0	18,093.4
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	6,652.9	6,674.6
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	6,652.9	6,674.6
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	7,576.4	7,368.0
Corporate Bonds [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	7,576.4	7,368.0
Canadian Provincial 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	693.5	655.9
Canadian Provincial Bonds [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	693.5	655.9
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	616.8	548.4
Asset-Backed Securities [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	616.8	548.4
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	555.4	552.9
Municipal Bonds [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	555.4	552.9
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	1,063.4	1,017.0
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	1,063.4	1,017.0
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	21.8	20.6
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	1,236.8	1,256.0
Other Securities [Member] | Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	1,258.6	1,276.6
Corporate Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	558.1	117.3
Funds Held For Clients [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities - Fair Value	$ 17,858.9	$ 17,976.1