Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 1,223.2	$ 1,188.6
Short-term investments: Available-for-sale securities	411.2	790.8
Short-term investments: Trading securities	63.3	57.6
Total short-term investments	474.5	848.4
Short term derivatives	14.4	9.5
Long-term investments	44.4	116.0
Long-term derivatives	7.5
Total	1,764.0	2,162.5
Short-term derivatives	23.7	18.9
Long-term derivatives	1.1	3.0
Total derivatives	24.8	21.9
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,223.2	1,188.6
Short-term investments: Available-for-sale securities	205.0	459.7
Short-term investments: Trading securities	63.3	57.6
Total short-term investments	268.3	517.3
Short term derivatives	0	0
Long-term investments	0	0
Long-term derivatives	0
Total	1,491.5	1,705.9
Short-term derivatives	0	0
Long-term derivatives	0	0
Total derivatives	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Short-term investments: Available-for-sale securities	206.2	331.1
Short-term investments: Trading securities	0	0
Total short-term investments	206.2	331.1
Short term derivatives	14.4	9.5
Long-term investments	30.5	97.4
Long-term derivatives	7.5
Total	258.6	438.0
Short-term derivatives	23.7	18.9
Long-term derivatives	1.1	3.0
Total derivatives	24.8	21.9
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Short-term investments: Available-for-sale securities	0	0
Short-term investments: Trading securities	0	0
Total short-term investments	0	0
Short term derivatives	0	0
Long-term investments	13.9	18.6
Long-term derivatives	0
Total	13.9	18.6
Short-term derivatives	0	0
Long-term derivatives	0	0
Total derivatives	0	0
Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	20.0	80.0
Long-term investments	4.0	14.0
Agency Obligations [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Long-term investments	0	0
Agency Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	20.0	80.0
Long-term investments	4.0	14.0
Agency Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Long-term investments	0	0
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	59.0	103.9
Commercial Paper [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	59.0	103.9
Commercial Paper [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	89.6	84.3
Long-term investments	24.0	61.3
Corporate Debt Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Long-term investments	0	0
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	89.6	84.3
Long-term investments	24.0	61.3
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Long-term investments	0	0
Government Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	205.0	459.7
Government Treasury Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	205.0	459.7
Government Treasury Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Government Treasury Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term investments	13.9	18.6
Auction Rate Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term investments	0	0
Auction Rate Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term investments	0	0
Auction Rate Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term investments	13.9	18.6
Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	37.6	62.9
Long-term investments	2.5	22.1
Certificates Of Deposit [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Long-term investments	0	0
Certificates Of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	37.6	62.9
Long-term investments	2.5	22.1
Certificates Of Deposit [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments: Available-for-sale securities	0	0
Long-term investments	$ 0	$ 0