BALANCE SHEET COMPONENTS - Available-for-Sale Securities (Detail) - USD ($) $ in Millions	Mar. 30, 2018	Sep. 29, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 10.7	$ 60.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	10.7	60.1
Original CPTC loans
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		47.4
Gross Unrealized Gains		0.0
Gross Unrealized Losses		0.0
Fair Value		47.4
DRTC Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		8.3
Gross Unrealized Gains		0.0
Gross Unrealized Losses		0.0
Fair Value		8.3
APTC Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	6.1
Gross Unrealized Gains	0.0
Gross Unrealized Losses	0.0
Fair Value	6.1
GPTC Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	4.6	4.4
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	$ 4.6	$ 4.4

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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