Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Sep. 30, 2018
Assets:
Total short-term investments	$ 72.1	$ 181.5
Total Assets	5,081.8	9,240.4
Liabilities:
Financial Liabilities Fair Value Disclosure	25.5	50.0
Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	4,763.3	8,756.3
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.3	106.2
Equity Securities, FV-NI	66.8	75.3
Total short-term investments	72.1	181.5
Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	13.5	24.5
Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	222.6	267.7
Other Long-Term Assets [Member]
Assets:
Derivative assets	10.3	10.4
Accrued Liabilities [Member]
Liabilities:
Derivative liabilities	11.3	6.5
Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities	14.2	43.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total Assets	4,936.4	8,940.9
Liabilities:
Financial Liabilities Fair Value Disclosure	0.6	0.4
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	4,763.3	8,756.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Equity Securities, FV-NI	66.8	75.3
Total short-term investments	66.8	75.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	0.1	1.2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	106.2	108.1
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities	0.6	0.4
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total Assets	139.7	293.6
Liabilities:
Financial Liabilities Fair Value Disclosure	24.9	49.6
Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.3	106.2
Equity Securities, FV-NI	0.0	0.0
Total short-term investments	5.3	106.2
Significant Other Observable Inputs (Level 2) [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	13.4	23.3
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	110.7	153.7
Significant Other Observable Inputs (Level 2) [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets	10.3	10.4
Significant Other Observable Inputs (Level 2) [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities	10.7	6.1
Significant Other Observable Inputs (Level 2) [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities	14.2	43.5
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Total Assets	5.7	5.9
Liabilities:
Financial Liabilities Fair Value Disclosure	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Equity Securities, FV-NI	0.0	0.0
Total short-term investments	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.7	5.9
Significant Unobservable Inputs (Level 3) [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities	0.0	0.0
Agency Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		5.9
Agency Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		0.0
Agency Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		5.9
Agency Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		0.0
Commercial Paper [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.2	8.4
Commercial Paper [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.2	8.4
Commercial Paper [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Corporate Debt Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	4.9	91.8
Corporate Debt Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	101.6	114.5
Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	4.9	91.8
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	101.6	114.5
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Foreign Government Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		3.6
Foreign Government Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		0.0
Foreign Government Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		3.6
Foreign Government Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		0.0
U.S. Government Treasury Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	106.2	108.1
U.S. Government Treasury Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	106.2	108.1
U.S. Government Treasury Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
U.S. Government Treasury Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
State and Local Government Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.0	4.8
State and Local Government Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
State and Local Government Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.0	4.8
State and Local Government Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Auction Rate Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.7	5.9
Auction Rate Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Auction Rate Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Auction Rate Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.7	5.9
Mortgage and Other Asset-backed Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.2	6.0
Mortgage and Other Asset-backed Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	4.1	24.9
Mortgage and Other Asset-backed Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Mortgage and Other Asset-backed Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Mortgage and Other Asset-backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.2	6.0
Mortgage and Other Asset-backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	4.1	24.9
Mortgage and Other Asset-backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Mortgage and Other Asset-backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	$ 0.0	$ 0.0