Pension and Post-Retirement Plans (Components of Net Pension Expense and Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 15, 2013	Jun. 16, 2012	Jun. 15, 2013	Jun. 16, 2012
Pension [Member]
Components of net pension expense:
Estimated return on plan assets	$ (24.9)	$ (23.4)	$ (49.8)	$ (46.9)
Service cost	9.7	10.3	19.5	19.5
Interest cost	19.7	21.3	39.4	42.6
Amortization of prior service cost (credit)	3.0	3.6	5.9	7.3
Amortization of unrecognized losses	18.0	16.7	35.9	33.4
Total	25.5	28.5	50.9	55.9
Other Post-Retirement Benefits [Member]
Components of net pension expense:
Estimated return on plan assets	0	0	0	0
Service cost	0.1	0.1	0.3	0.3
Interest cost	0.7	0.8	1.4	1.7
Amortization of prior service cost (credit)	0	0	(0.1)	(0.1)
Amortization of unrecognized losses	0.2	0.1	0.5	0.2
Total	$ 1.0	$ 1.0	$ 2.1	$ 2.1