Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 27, 2020	Sep. 27, 2020
Assets:
Total short-term investments	$ 235.5	$ 281.2
Total Assets	5,532.7	4,941.1
Liabilities:
Financial Liabilities Fair Value Disclosure	80.6	86.6
Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	5,028.1	4,350.9
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	169.6	216.3
Equity Securities, FV-NI	65.9	64.9
Total short-term investments	235.5	281.2
Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, current	24.7	15.6
Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	190.9	206.1
Other Long-Term Assets [Member]
Assets:
Derivative assets, Noncurrent	53.5	87.3
Accrued Liabilities [Member]
Liabilities:
Derivative liabilities, Current	13.2	7.3
Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities, Noncurrent	67.4	79.3
Auction Rate Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.7	5.7
Certificates of Deposit | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	1.6	1.6
Commercial Paper [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	71.8	66.8
Corporate Debt Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	78.5	123.6
Corporate Debt Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	82.6	82.6
Foreign Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		8.5
Mortgage and Other Asset-backed Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	16.7	15.8
Mortgage and Other Asset-backed Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	9.8	19.3
State and Local Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	1.0
State and Local Government Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	2.6	3.6
U.S. Government Treasury Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	90.2	94.9
Fair Value, Inputs, Level 1 [Member]
Assets:
Total Assets	5,198.8	4,514.3
Liabilities:
Financial Liabilities Fair Value Disclosure	0.8	2.0
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	5,028.1	4,350.9
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Equity Securities, FV-NI	65.9	64.9
Total short-term investments	65.9	64.9
Fair Value, Inputs, Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, current	14.6	3.6
Fair Value, Inputs, Level 1 [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	90.2	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	0.8	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 [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Commercial Paper [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Foreign Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		0.0
Fair Value, Inputs, Level 1 [Member] | Mortgage and Other Asset-backed Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Mortgage and Other Asset-backed Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | State and Local Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0
Fair Value, Inputs, Level 1 [Member] | State and Local Government Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | U.S. Government Treasury Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	90.2	94.9
Fair Value, Inputs, Level 2 [Member]
Assets:
Total Assets	328.2	421.1
Liabilities:
Financial Liabilities Fair Value Disclosure	79.8	84.6
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	169.6	216.3
Equity Securities, FV-NI	0.0	0.0
Total short-term investments	169.6	216.3
Fair Value, Inputs, Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets:
Derivative assets, current	10.1	12.0
Fair Value, Inputs, Level 2 [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	95.0	105.5
Fair Value, Inputs, Level 2 [Member] | Other Long-Term Assets [Member]
Assets:
Derivative assets, Noncurrent	53.5	87.3
Fair Value, Inputs, Level 2 [Member] | Accrued Liabilities [Member]
Liabilities:
Derivative liabilities, Current	12.4	5.4
Fair Value, Inputs, Level 2 [Member] | Other Long-Term Liabilities [Member]
Liabilities:
Derivative liabilities, Noncurrent	67.4	79.2
Fair Value, Inputs, Level 2 [Member] | Auction Rate Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	1.6	1.6
Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	71.8	66.8
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	78.5	123.6
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	82.6	82.6
Fair Value, Inputs, Level 2 [Member] | Foreign Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		8.5
Fair Value, Inputs, Level 2 [Member] | Mortgage and Other Asset-backed Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	16.7	15.8
Fair Value, Inputs, Level 2 [Member] | Mortgage and Other Asset-backed Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	9.8	19.3
Fair Value, Inputs, Level 2 [Member] | State and Local Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	1.0
Fair Value, Inputs, Level 2 [Member] | State and Local Government Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	2.6	3.6
Fair Value, Inputs, Level 2 [Member] | U.S. Government Treasury Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member]
Assets:
Total Assets	5.7	5.7
Liabilities:
Financial Liabilities Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Assets:
Cash and cash equivalents	0.0	0.0
Fair Value, 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
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:
Debt Securities, Available-for-sale	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 [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	5.7	5.7
Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Commercial Paper [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Foreign Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale		0.0
Fair Value, Inputs, Level 3 [Member] | Mortgage and Other Asset-backed Securities [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Mortgage and Other Asset-backed Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | State and Local Government Obligations [Member] | Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0
Fair Value, Inputs, Level 3 [Member] | State and Local Government Obligations [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | U.S. Government Treasury Securities [Member] | Long-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	$ 0.0	$ 0.0