Retirement Benefits (Fair Values Of Pension Benefit Assets And Other Benefit Assets By Asset Category And Level Inputs) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	$ 663.1	$ 524.7	$ 522.7	$ 548.3
Partnership Interests [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	221.2	113.7	118.6	122.2
Insurance Company Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	173.4	173.3	174.2	187.7
Life Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	268.5	237.7	229.9	$ 238.4
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2,012.3	1,887.8	1,865.2
Pension Benefits [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1,029.4	1,046.7
Pension Benefits [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	575.1	552.5
Pension Benefits [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	394.2	285.8
Pension Benefits [Member] | U.S. Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	589.2	565.8
Pension Benefits [Member] | U.S. Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	584.4	561.4
Pension Benefits [Member] | U.S. Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	4.8	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	178.7	264.5
Pension Benefits [Member] | Foreign Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	178.7	264.5
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	39.4	36.6
Pension Benefits [Member] | Mutual Funds [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	39.4	36.6
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	226.9	183.9
Pension Benefits [Member] | Government Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	226.9	183.9
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	376.5	385.9
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	376.5	385.9
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	139.9	134.7
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	139.9	134.7
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	53.9	27.5
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	53.9	27.5
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	220.8	112.5
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	220.8	112.5
Pension Benefits [Member] | Insurance Company Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	173.4	173.3
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	173.4	173.3
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	1,998.7	1,885.0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	356.3	331.8	$ 328.4
Other Benefits [Member] | U.S. Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	10.5	13.2
Other Benefits [Member] | U.S. Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	10.3	13.0
Other Benefits [Member] | U.S. Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0.2	0.2
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	3.3	5.4
Other Benefits [Member] | Foreign Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	3.3	5.4
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	47.8	47.1
Other Benefits [Member] | Mutual Funds [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	47.8	47.1
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	2.5	2.7
Other Benefits [Member] | Government Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2.5	2.7
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	5.2	7.9
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	5.2	7.9
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	4.7	5.8
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	4.7	5.8
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	0.5	1.0
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	0.5	1.0
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	0.4	1.2
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	0.4	1.2
Other Benefits [Member] | Life Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	268.5	237.7
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	268.5	237.7
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	11.4	9.8
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	11.4	9.8
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
Other 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	354.8	331.8
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	63.9	68.2
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	22.0	24.7
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	$ 268.9	$ 238.9