Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 10,879.7	$ 10,616.2	$ 11,091.0	$ 10,508.3
Net Change	325.4	185.5	565.1	293.9
Ending balance	11,382.2	10,805.5	11,382.2	10,805.5
TOTAL
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	45.0	(345.3)	(194.7)	(453.7)
Ending balance	370.4	(159.8)	370.4	(159.8)
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	313.7	(29.3)	114.0	(114.9)
Net Change	318.1	162.4	517.8	248.0
Ending balance	631.8	133.1	631.8	133.1
NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	3.6	(0.3)	(3.7)	4.0
Net Change	(3.3)	4.8	4.0	0.5
Ending balance	0.3	4.5	0.3	4.5
NET FOREIGN CURRENCY ADJUSTMENT
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	143.5	82.7	117.8	67.9
Net Change	2.0	14.1	27.7	28.9
Ending balance	145.5	96.8	145.5	96.8
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(415.8)	(398.4)	(422.8)	(410.7)
Net Change	8.6	4.2	15.6	16.5
Ending balance	$ (407.2)	$ (394.2)	$ (407.2)	$ (394.2)