Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Assets:
Total short-term investments	$ 76.6	$ 181.5
Total Assets	2,414.3	9,240.4
Liabilities:
Financial Liabilities Fair Value Disclosure	56.3	50.0
Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	2,055.1	8,756.3
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	12.0	106.2
Equity Securities, FV-NI	64.6	75.3
Total short-term investments	76.6	181.5
Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	19.9	24.5
Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	251.9	267.7
Other Long-Term Assets [Member]
Assets:
Derivative assets	10.8	10.4
Accrued Liabilities [Member]
Liabilities:
Derivative liabilities	11.8	6.5
Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities	44.5	43.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total Assets	2,229.6	8,940.9
Liabilities:
Financial Liabilities Fair Value Disclosure	1.4	0.4
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	2,055.1	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	64.6	75.3
Total short-term investments	64.6	75.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	0.2	1.2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	109.7	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	1.4	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	179.0	293.6
Liabilities:
Financial Liabilities Fair Value Disclosure	54.9	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	12.0	106.2
Equity Securities, FV-NI	0.0	0.0
Total short-term investments	12.0	106.2
Significant Other Observable Inputs (Level 2) [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets	19.7	23.3
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	136.5	153.7
Significant Other Observable Inputs (Level 2) [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets	10.8	10.4
Significant Other Observable Inputs (Level 2) [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities	10.4	6.1
Significant Other Observable Inputs (Level 2) [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities	44.5	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	6.0	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	0.0
Agency Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	6.0	5.9
Agency Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	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	4.8	91.8
Corporate Debt Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	119.0	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	4.8	91.8
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	119.0	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] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	3.7
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] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0
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] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	3.7
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] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0
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	109.7	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	109.7	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	4.9	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	4.9	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	3.3	6.0
Mortgage and Other Asset-backed Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	6.6	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	3.3	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	6.6	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