Retirement Benefits and Postemployment Benefits (Schedule of plans with accumulated benefit obiligations in excess of plan assets) (Details) (USD $) In Millions, unless otherwise specified	May 26, 2013	May 27, 2012
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets [Abstract]
Projected benefit obligation	$ 396.9	$ 423.4
Accumulated benefit obligation	346.6	361.5
Plan assets at fair value	9.5	53.0
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets [Abstract]
Projected benefit obligation	0	0
Accumulated benefit obligation	1,132.9	1,129.0
Plan assets at fair value	436.9	358.8
Postemployment Benefit Plans [Member]
Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets [Abstract]
Projected benefit obligation	0	0
Accumulated benefit obligation	145.4	141.3
Plan assets at fair value	$ 0	$ 0