Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Oct. 01, 2017
Assets [Abstract]
Total short-term investments	$ 181.5	$ 228.6
Long-term investments: Available-for-sale securities	267.7	542.3
Total assets	9,240.4	3,271.0
Liabilities [Abstract]
Total liabilities	50.0	38.5
Cash and cash equivalents [Member]
Assets [Abstract]
Cash and cash equivalents	8,756.3	2,462.3
Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	106.2	151.7
Short-term investments: Trading securities	75.3	76.9
Total short-term investments	181.5	228.6
Prepaid expenses and other current assets [Member]
Assets [Abstract]
Prepaid expenses and other current assets: Derivative assets	24.5	13.4
Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	267.7	542.3
Other long-term assets [Member]
Assets [Abstract]
Other long-term assets: Derivative assets	10.4	24.4
Accrued liabilities [Member]
Liabilities [Abstract]
Accrued liabilities: Derivative liabilities	6.5	16.4
Other long-term liabilities [Member]
Liabilities [Abstract]
Other long-term liabilities: Derivative liabilities	43.5	22.1
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Total assets	8,940.9	2,748.1
Liabilities [Abstract]
Total liabilities	0.4	2.5
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Cash and cash equivalents [Member]
Assets [Abstract]
Cash and cash equivalents	8,756.3	2,462.3
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0	81.4
Short-term investments: Trading securities	75.3	76.9
Total short-term investments	75.3	158.3
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Prepaid expenses and other current assets [Member]
Assets [Abstract]
Prepaid expenses and other current assets: Derivative assets	1.2	0.1
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	108.1	127.4
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Other long-term assets [Member]
Assets [Abstract]
Other long-term assets: Derivative assets	0.0	0.0
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Accrued liabilities [Member]
Liabilities [Abstract]
Accrued liabilities: Derivative liabilities	0.4	2.5
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Other long-term liabilities [Member]
Liabilities [Abstract]
Other long-term liabilities: Derivative liabilities	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Total assets	293.6	517.0
Liabilities [Abstract]
Total liabilities	49.6	36.0
Significant Other Observable Inputs (Level 2) [Member] | Cash and cash equivalents [Member]
Assets [Abstract]
Cash and cash equivalents	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	106.2	70.3
Short-term investments: Trading securities	0.0	0.0
Total short-term investments	106.2	70.3
Significant Other Observable Inputs (Level 2) [Member] | Prepaid expenses and other current assets [Member]
Assets [Abstract]
Prepaid expenses and other current assets: Derivative assets	23.3	13.3
Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	153.7	409.0
Significant Other Observable Inputs (Level 2) [Member] | Other long-term assets [Member]
Assets [Abstract]
Other long-term assets: Derivative assets	10.4	24.4
Significant Other Observable Inputs (Level 2) [Member] | Accrued liabilities [Member]
Liabilities [Abstract]
Accrued liabilities: Derivative liabilities	6.1	13.9
Significant Other Observable Inputs (Level 2) [Member] | Other long-term liabilities [Member]
Liabilities [Abstract]
Other long-term liabilities: Derivative liabilities	43.5	22.1
Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Total assets	5.9	5.9
Liabilities [Abstract]
Total liabilities	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Cash and cash equivalents [Member]
Assets [Abstract]
Cash and cash equivalents	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0	0.0
Short-term investments: Trading securities	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 [Abstract]
Prepaid expenses and other current assets: Derivative assets	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	5.9	5.9
Significant Unobservable Inputs (Level 3) [Member] | Other long-term assets [Member]
Assets [Abstract]
Other long-term assets: Derivative assets	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Accrued liabilities [Member]
Liabilities [Abstract]
Accrued liabilities: Derivative liabilities	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Other long-term liabilities [Member]
Liabilities [Abstract]
Other long-term liabilities: Derivative liabilities	0.0	0.0
Certificates of Deposit [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		2.3
Certificates of Deposit [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
Certificates of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		2.3
Certificates of Deposit [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
Agency obligations [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		7.5
Agency obligations [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	5.9	21.8
Agency obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
Agency obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Agency obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		7.5
Agency obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	5.9	21.8
Agency obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
Agency obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Commercial Paper [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	8.4	2.0
Commercial Paper [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0	0.0
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	8.4	2.0
Commercial Paper [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0	0.0
Corporate debt securities [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	91.8	49.4
Corporate debt securities [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	114.5	207.4
Corporate debt securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0	0.0
Corporate debt securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Corporate debt securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	91.8	49.4
Corporate debt securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	114.5	207.4
Corporate debt securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0	0.0
Corporate debt securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Auction rate securities [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	5.9	5.9
Auction rate securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Auction rate securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Auction rate securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	5.9	5.9
Foreign government obligations [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		7.1
Foreign government obligations [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	3.6	17.1
Foreign government obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
Foreign government obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Foreign government obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		7.1
Foreign government obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	3.6	17.1
Foreign government obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
Foreign government obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
U.S. government treasury securities [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		81.4
U.S. government treasury securities [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	108.1	127.4
U.S. government treasury securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		81.4
U.S. government treasury securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	108.1	127.4
U.S. government treasury securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
U.S. government treasury securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
U.S. government treasury securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
U.S. government treasury securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
State and local government obligations [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		2.0
State and local government obligations [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	4.8	7.0
State and local government obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
State and local government obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
State and local government obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		2.0
State and local government obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	4.8	7.0
State and local government obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities		0.0
State and local government obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Mortgage and other asset-backed securities [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	6.0
Mortgage and other asset-backed securities [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	24.9	155.7
Mortgage and other asset-backed securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	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 [Abstract]
Long-term investments: Available-for-sale securities	0.0	0.0
Mortgage and other asset-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	6.0
Mortgage and other asset-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	24.9	155.7
Mortgage and other asset-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Short-term investments [Member]
Assets [Abstract]
Short-term investments: Available-for-sale securities	0.0
Mortgage and other asset-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Long-term investments [Member]
Assets [Abstract]
Long-term investments: Available-for-sale securities	$ 0.0	$ 0.0