Retirement Benefits (Schedule of Components in Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items] [Line Items]
Accrued retirement benefits	$ (3,513.9)	$ (2,453.9)
Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items] [Line Items]
Sundry	106.8	29.7
Other current liabilities	(64.8)	(68.0)
Accrued retirement benefits	(3,295.9)	(2,237.9)
Accumulated other comprehensive (income) loss before income taxes	5,660.7	4,937.4
Net amount recognized	2,406.8	2,661.2
Unrecognized net actuarial loss	(366.1)
Unrecognized prior service (benefit) cost	5.1
Total	371.2
Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items] [Line Items]
Sundry	869.0	689.3
Other current liabilities	(7.1)	(6.7)
Accrued retirement benefits	(218.0)	(216.0)
Accumulated other comprehensive (income) loss before income taxes	(213.0)	(66.3)
Net amount recognized	430.9	$ 400.3
Unrecognized net actuarial loss	(9.5)
Unrecognized prior service (benefit) cost	(81.3)
Total	$ (71.8)