Retirement Benefits (Reconciliation Of The Beginning And Ending Balances Of Plan Assets Measured At Fair Value Using Level III Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	$ 522.7	$ 548.3	$ 587.7
Actual return on plan assets, relating to assets still held at the reporting date	4.2	(18.4)	4.4
Purchases	26.7	17.9	20.0
Sales	(28.9)	(25.1)	(63.8)
Ending balance	524.7	522.7	548.3
Partnership Interests [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	118.6	122.2	160.3
Actual return on plan assets, relating to assets still held at the reporting date	(3.5)	(5.9)	(5.4)
Purchases	17.8	10.9	8.4
Sales	(19.2)	(8.6)	(41.1)
Ending balance	113.7	118.6	122.2
Insurance Company Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	174.2	187.7	197.4
Actual return on plan assets, relating to assets still held at the reporting date	(3.1)	(5.7)	1.4
Purchases	8.9	7.0	11.6
Sales	(6.7)	(14.8)	(22.7)
Ending balance	173.3	174.2	187.7
Life Insurance Contracts [Member]
Change in Fair Value of Plan Assets, Level 3 Reconciliation
Beginning balance	229.9	238.4	230.0
Actual return on plan assets, relating to assets still held at the reporting date	10.8	(6.8)	8.4
Purchases	0.0	0.0	0.0
Sales	(3.0)	(1.7)	0.0
Ending balance	$ 237.7	$ 229.9	$ 238.4