Fair Value Measurements (Tables)

6 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Assets And Liabilities Measured At Fair Value On A Recurring Basis

			Fair Value Measurements at Reporting Date Using
	Balance at March 31, 2019		Quoted Prices in Active Markets for  Identical Assets (Level 1)		Significant  Other Observable  Inputs (Level 2)		Significant Unobservable  Inputs (Level 3)
Assets:
Cash and cash equivalents	$	2,055.1	$	2,055.1	$	—	$	—
Short-term investments:
Available-for-sale debt securities
Commercial paper	0.2		—		0.2		—
Corporate debt securities	4.8		—		4.8		—
Foreign government obligations	3.7		—		3.7		—
Mortgage and other asset-backed securities	3.3		—		3.3		—
Total available-for-sale debt securities	12.0		—		12.0		—
Marketable equity securities	64.6		64.6		—		—
Total short-term investments	76.6		64.6		12.0		—
Prepaid expenses and other current assets:
Derivative assets	19.9		0.2		19.7		—
Long-term investments:
Available-for-sale debt securities
Agency obligations	6.0		—		6.0		—
Corporate debt securities	119.0		—		119.0		—
Auction rate securities	5.7		—		—		5.7
U.S. government treasury securities	109.7		109.7		—		—
State and local government obligations	4.9		—		4.9		—
Mortgage and other asset-backed securities	6.6		—		6.6		—
Total long-term investments	251.9		109.7		136.5		5.7
Other long-term assets:
Derivative assets	10.8		—		10.8		—
Total assets	$	2,414.3	$	2,229.6	$	179.0	$	5.7
Liabilities:
Accrued liabilities:
Derivative liabilities	$	11.8	$	1.4	$	10.4	$	—
Other long-term liabilities:
Derivative liabilities	44.5		—		44.5		—
Total liabilities	$	56.3	$	1.4	$	54.9	$	—

			Fair Value Measurements at Reporting Date Using
	Balance at September 30, 2018		Quoted Prices in Active Markets for  Identical Assets (Level 1)		Significant  Other Observable  Inputs (Level 2)		Significant Unobservable  Inputs (Level 3)
Assets:
Cash and cash equivalents	$	8,756.3	$	8,756.3	$	—	$	—
Short-term investments:
Available-for-sale debt securities
Commercial paper	8.4		—		8.4		—
Corporate debt securities	91.8		—		91.8		—
Mortgage and other asset-backed securities	6.0		—		6.0		—
Total available-for-sale debt securities	106.2		—		106.2		—
Marketable equity securities	75.3		75.3		—		—
Total short-term investments	181.5		75.3		106.2		—
Prepaid expenses and other current assets:
Derivative assets	24.5		1.2		23.3		—
Long-term investments:
Available-for-sale debt securities
Agency obligations	5.9		—		5.9		—
Corporate debt securities	114.5		—		114.5		—
Auction rate securities	5.9		—		—		5.9
Foreign government obligations	3.6		—		3.6		—
U.S. government treasury securities	108.1		108.1		—		—
State and local government obligations	4.8		—		4.8		—
Mortgage and other asset-backed securities	24.9		—		24.9		—
Total long-term investments	267.7		108.1		153.7		5.9
Other long-term assets:
Derivative assets	10.4		—		10.4		—
Total assets	$	9,240.4	$	8,940.9	$	293.6	$	5.9
Liabilities:
Accrued liabilities:
Derivative liabilities	$	6.5	$	0.4	$	6.1	$	—
Other long-term liabilities:
Derivative liabilities	43.5		—		43.5		—
Total liabilities	$	50.0	$	0.4	$	49.6	$	—