Employee Benefits Schedule of fair value of financial assets for pension and postretirement benefits (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 737.2	$ 672.0
Corporate bonds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.5	1.7
U.S. government securities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	12.9	1.6
Fixed income registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	114.9	110.7
Inflation protection registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	34.5	29.4
Domestic equity registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.6	2.0
Cash equivalent commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	6.7	3.5
Domestic equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	275.8	256.2
Foreign equity growth commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	41.2	42.9
Foreign equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	77.8	76.0
Corporate debt commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	91.0	72.1
Inflation protection commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	33.1	28.8
Foreign equity growth 103-12 investment entities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	46.2	47.1
Level 1 [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	151.0	142.1
Level 1 [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | U.S. government securities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Fixed income registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	114.9	110.7
Level 1 [Member] | Inflation protection registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	34.5	29.4
Level 1 [Member] | Domestic equity registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.6	2.0
Level 1 [Member] | Cash equivalent commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Domestic equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Foreign equity growth commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Foreign equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Corporate debt commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Inflation protection commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 1 [Member] | Foreign equity growth 103-12 investment entities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 2 [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	586.2	529.9
Level 2 [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.5	1.7
Level 2 [Member] | U.S. government securities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	12.9	1.6
Level 2 [Member] | Fixed income registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 2 [Member] | Inflation protection registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 2 [Member] | Domestic equity registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Level 2 [Member] | Cash equivalent commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	6.7	3.5
Level 2 [Member] | Domestic equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	275.8	256.2
Level 2 [Member] | Foreign equity growth commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	41.2	42.9
Level 2 [Member] | Foreign equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	77.8	76.0
Level 2 [Member] | Corporate debt commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	91.0	72.1
Level 2 [Member] | Inflation protection commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	33.1	28.8
Level 2 [Member] | Foreign equity growth 103-12 investment entities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 46.2	$ 47.1