Retirement Benefits (Reconciliation Of The Benefit Obligation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Reconciliation of benefit obligation
Benefit obligation at beginning of year	$ 1,824.9	$ 1,833.3
Service cost	10.1	11.6	$ 13.1
Interest cost	66.3	68.5	68.2
Actuarial loss (gain)	103.7	32.2
Benefits paid	(132.6)	(120.7)
Benefit obligation at end of year	1,872.4	1,824.9	1,833.3
Other Benefits [Member]
Reconciliation of benefit obligation
Benefit obligation at beginning of year	565.2	578.7
Service cost	1.4	1.6	2.1
Interest cost	20.8	22.4	23.4
Actuarial loss (gain)	(39.2)	(4.2)
Benefits paid	(24.0)	(33.3)
Benefit obligation at end of year	$ 524.2	$ 565.2	$ 578.7