Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 28, 2021	Sep. 27, 2020
Assets:
Total short-term investments	$ 123.0	$ 281.2
Total Assets	4,406.6	4,941.1
Liabilities:
Total liabilities	26.9	86.6
Cash and cash equivalents
Assets:
Cash and cash equivalents	3,880.7	4,350.9
Short-term Investments [Member]
Assets:
Available-for-sale debt securities	53.5	216.3
Marketable equity securities	69.5	64.9
Total short-term investments	123.0	281.2
Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, Current	22.0	15.6
Long-term Investments [Member]
Assets:
Available-for-sale debt securities	284.8	206.1
Other Long-Term Assets [Member]
Assets:
Derivative assets, Noncurrent	96.1	87.3
Accrued Liabilities [Member]
Liabilities:
Derivative liabilities, Current	13.3	7.3
Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities, Noncurrent	13.6	79.3
Auction rate securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	5.7	5.7
Certificates of deposit | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		1.6
Commercial paper | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	38.5	66.8
Corporate debt securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	14.0	123.6
Corporate debt securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	167.4	82.6
Foreign government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	4.0
Foreign Government Short-term Debt Securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		8.5
Mortgage and other asset-backed securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		15.8
Mortgage and other asset-backed securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	18.0	19.3
State and local government obligations | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	1.0
State and local government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	4.1	3.6
U.S. government treasury securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	85.6	94.9
Fair Value, Inputs, Level 1 [Member]
Assets:
Total Assets	4,049.0	4,514.3
Liabilities:
Total liabilities	0.2	2.0
Fair Value, Inputs, Level 1 [Member] | Cash and cash equivalents
Assets:
Cash and cash equivalents	3,880.7	4,350.9
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Marketable equity securities	69.5	64.9
Total short-term investments	69.5	64.9
Fair Value, Inputs, Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, Current	13.2	3.6
Fair Value, Inputs, Level 1 [Member] | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	85.6	94.9
Fair Value, Inputs, Level 1 [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets, Noncurrent	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities, Current	0.2	1.9
Fair Value, Inputs, Level 1 [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities, Noncurrent	0.0	0.1
Fair Value, Inputs, Level 1 [Member] | Auction rate securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Certificates of deposit | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		0.0
Fair Value, Inputs, Level 1 [Member] | Commercial paper | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Corporate debt securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Corporate debt securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Foreign government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0
Fair Value, Inputs, Level 1 [Member] | Foreign Government Short-term Debt Securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		0.0
Fair Value, Inputs, Level 1 [Member] | Mortgage and other asset-backed securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		0.0
Fair Value, Inputs, Level 1 [Member] | Mortgage and other asset-backed securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | State and local government obligations | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0
Fair Value, Inputs, Level 1 [Member] | State and local government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | U.S. government treasury securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	85.6	94.9
Fair Value, Inputs, Level 2 [Member]
Assets:
Total Assets	351.9	421.1
Liabilities:
Total liabilities	26.7	84.6
Fair Value, Inputs, Level 2 [Member] | Cash and cash equivalents
Assets:
Cash and cash equivalents	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	53.5	216.3
Marketable equity securities	0.0	0.0
Total short-term investments	53.5	216.3
Fair Value, Inputs, Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, Current	8.8	12.0
Fair Value, Inputs, Level 2 [Member] | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	193.5	105.5
Fair Value, Inputs, Level 2 [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets, Noncurrent	96.1	87.3
Fair Value, Inputs, Level 2 [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities, Current	13.1	5.4
Fair Value, Inputs, Level 2 [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities, Noncurrent	13.6	79.2
Fair Value, Inputs, Level 2 [Member] | Auction rate securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Certificates of deposit | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		1.6
Fair Value, Inputs, Level 2 [Member] | Commercial paper | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	38.5	66.8
Fair Value, Inputs, Level 2 [Member] | Corporate debt securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	14.0	123.6
Fair Value, Inputs, Level 2 [Member] | Corporate debt securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	167.4	82.6
Fair Value, Inputs, Level 2 [Member] | Foreign government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	4.0
Fair Value, Inputs, Level 2 [Member] | Foreign Government Short-term Debt Securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		8.5
Fair Value, Inputs, Level 2 [Member] | Mortgage and other asset-backed securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		15.8
Fair Value, Inputs, Level 2 [Member] | Mortgage and other asset-backed securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	18.0	19.3
Fair Value, Inputs, Level 2 [Member] | State and local government obligations | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	1.0
Fair Value, Inputs, Level 2 [Member] | State and local government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	4.1	3.6
Fair Value, Inputs, Level 2 [Member] | U.S. government treasury securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 3 [Member]
Assets:
Total Assets	5.7	5.7
Liabilities:
Total liabilities	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Cash and cash equivalents
Assets:
Cash and cash equivalents	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Marketable equity securities	0.0	0.0
Total short-term investments	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, Current	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	5.7	5.7
Fair Value, Inputs, Level 3 [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets, Noncurrent	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities, Current	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities, Noncurrent	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Auction rate securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	5.7	5.7
Fair Value, Inputs, Level 3 [Member] | Certificates of deposit | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		0.0
Fair Value, Inputs, Level 3 [Member] | Commercial paper | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Corporate debt securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Corporate debt securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Foreign government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0
Fair Value, Inputs, Level 3 [Member] | Foreign Government Short-term Debt Securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		0.0
Fair Value, Inputs, Level 3 [Member] | Mortgage and other asset-backed securities | Short-term Investments [Member]
Assets:
Available-for-sale debt securities		0.0
Fair Value, Inputs, Level 3 [Member] | Mortgage and other asset-backed securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | State and local government obligations | Short-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0
Fair Value, Inputs, Level 3 [Member] | State and local government obligations | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | U.S. government treasury securities | Long-term Investments [Member]
Assets:
Available-for-sale debt securities	$ 0.0	$ 0.0