Acquisitions (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 25, 2016 USD ($)	Mar. 27, 2015 USD ($) acquisition	Mar. 25, 2016 USD ($)	Mar. 27, 2015 USD ($) acquisition	Sep. 25, 2015
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired	$ 128	$ 373	$ 314	$ 525
Consideration transferred	166
Cash balance acquired in the acquisition of a business	27	6		26
Cash Held in Escrow from Acquisition		$ 5		$ 8
Number of Businesses Acquired | acquisition		6		11
Noncontrolling interest related to acquisitions and divestitures				$ 29
ShopperTrak [Member]
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired	176
Consideration transferred	182
Cash balance acquired in the acquisition of a business	6
UAE [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	99		99
cash paid to settle preexisting matters	5
Cash paid for pre-paid agency commission	6
Goodwill, Acquired During Period	136
Finite-lived Intangible Assets Acquired	99
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	$ 32		$ 32
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage	100.00%		100.00%
Gain Recognized upon purchasing remaining interest in joint venture	$ 111
Equity Method Investment, Ownership Percentage					49.00%
Circuito [Member]
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired			$ 10
IST [Member]
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired		$ 327
Cash balance acquired in the acquisition of a business		5
Businesses other than IST [Member]
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired		$ 46
Number of Businesses Acquired | acquisition		5		10