Fair Value Measurements (Pension Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 25, 2015	Dec. 26, 2014
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	$ 2,309	$ 2,504
Defined Benefit Plan, Fair Value of Plan Assets Excluding Assets Measured at NAV	1,393	1,528
Alternative Investments, Fair Value Disclosure	$ 916	976
Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment committee equity target allocation percentage of pension assets	70.00%
Pension plan assets at fair value	$ 1,626	1,715
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	$ 738	787
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment committee equity target allocation percentage of pension assets	30.00%
Pension plan assets at fair value	$ 641	740
Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	15	20
Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	8	1
Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	480	539
Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	132	164
Asset-backed securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	14	15
Derivatives and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	6	2
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	761	808
Defined Benefit Plan, Fair Value of Plan Assets Excluding Assets Measured at NAV	761	808
Level 1 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	738	787
Level 1 [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	15	20
Level 1 [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	8	1
Level 1 [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 [Member] | Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 [Member] | Asset-backed securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 [Member] | Derivatives and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	632	720
Defined Benefit Plan, Fair Value of Plan Assets Excluding Assets Measured at NAV	632	720
Level 2 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	480	539
Level 2 [Member] | Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	132	164
Level 2 [Member] | Asset-backed securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	14	15
Level 2 [Member] | Derivatives and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	6	2
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Defined Benefit Plan, Fair Value of Plan Assets Excluding Assets Measured at NAV	0	0
Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Asset-backed securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Derivatives and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	$ 0	$ 0