Retirement Benefits (Fair Values Of Pension Benefit Assets And Other Benefit Assets By Asset Category And Level Inputs) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	$ 524.7	$ 522.7	$ 548.3	$ 587.7
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1,887.8	1,865.2	1,985.0
Pension Benefits [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1,046.7	1,012.9
Pension Benefits [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	552.5	557.6
Pension Benefits [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	285.8	291.3
Pension Benefits [Member] | U.S. Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	565.8	547.2
Pension Benefits [Member] | U.S. Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	561.4	542.8
Pension Benefits [Member] | U.S. Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	4.4	4.4
Pension Benefits [Member] | U.S. Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Foreign Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	264.5	258.8
Pension Benefits [Member] | Foreign Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	264.5	258.8
Pension Benefits [Member] | Foreign Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Foreign Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	36.6	34.7
Pension Benefits [Member] | Mutual Funds [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	36.6	34.7
Pension Benefits [Member] | Mutual Funds [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Mutual Funds [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	183.9	176.6
Pension Benefits [Member] | Government Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	183.9	176.6
Pension Benefits [Member] | Government Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Government Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Corporate Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	385.9	364.0
Pension Benefits [Member] | Corporate Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Corporate Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	385.9	364.0
Pension Benefits [Member] | Corporate Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Asset-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	134.7	141.1
Pension Benefits [Member] | Asset-Backed Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Asset-Backed Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	134.7	141.1
Pension Benefits [Member] | Asset-Backed Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Common And Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	27.5	48.1
Pension Benefits [Member] | Common And Collective Trusts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Common And Collective Trusts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	27.5	48.1
Pension Benefits [Member] | Common And Collective Trusts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Partnership Interests [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	112.5	117.1
Pension Benefits [Member] | Partnership Interests [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Partnership Interests [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Partnership Interests [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	112.5	117.1
Pension Benefits [Member] | Insurance Company Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	173.3	174.2
Pension Benefits [Member] | Insurance Company Contracts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Insurance Company Contracts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Pension Benefits [Member] | Insurance Company Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	173.3	174.2
Pension Benefits [Member] | Treasury Futures Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.3
Pension Benefits [Member] | Treasury Futures Contracts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.3
Pension Benefits [Member] | Treasury Futures Contracts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0
Pension Benefits [Member] | Treasury Futures Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0
Pension Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1,885.0	1,861.8
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	331.8	328.4	$ 347.9
Other Benefits [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	68.2	64.6
Other Benefits [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	24.7	32.4
Other Benefits [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	238.9	231.4
Other Benefits [Member] | U.S. Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	13.2	17.1
Other Benefits [Member] | U.S. Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	13.0	16.8
Other Benefits [Member] | U.S. Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.2	0.3
Other Benefits [Member] | U.S. Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Foreign Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	5.4	7.4
Other Benefits [Member] | Foreign Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	5.4	7.4
Other Benefits [Member] | Foreign Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Foreign Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	47.1	36.6
Other Benefits [Member] | Mutual Funds [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	47.1	36.6
Other Benefits [Member] | Mutual Funds [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Mutual Funds [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2.7	3.8
Other Benefits [Member] | Government Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2.7	3.8
Other Benefits [Member] | Government Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Government Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Corporate Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	7.9	9.5
Other Benefits [Member] | Corporate Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Corporate Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	7.9	9.5
Other Benefits [Member] | Corporate Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Asset-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	5.8	7.7
Other Benefits [Member] | Asset-Backed Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Asset-Backed Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	5.8	7.7
Other Benefits [Member] | Asset-Backed Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Common And Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1.0	1.5
Other Benefits [Member] | Common And Collective Trusts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Common And Collective Trusts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1.0	1.5
Other Benefits [Member] | Common And Collective Trusts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Partnership Interests [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1.2	1.5
Other Benefits [Member] | Partnership Interests [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Partnership Interests [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Partnership Interests [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1.2	1.5
Other Benefits [Member] | Life Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	237.7	229.9
Other Benefits [Member] | Life Insurance Contracts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Life Insurance Contracts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Life Insurance Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	237.7	229.9
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	9.8	13.4
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.0	0.0
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	9.8	13.4
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	$ 0.0	$ 0.0