Employee Benefits Schedule of fair value of financial assets for pension and postretirement benefits (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 548.4	$ 423.9
Corporate bonds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.9	1.9
U.S. government securities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2.0	3.1
Fixed income registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	79.2	62.7
Inflation protection registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	25.5	19.5
Domestic equity registered investment companies [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.9	2.1
Cash equivalent commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	20.8	3.0
Domestic equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	185.9	145.8
Foreign equity growth commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	37.3	28.2
Foreign equity index commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	60.1	43.0
Corporate debt commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	72.8	65.7
Inflation protection commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	24.5	18.7
Foreign equity growth 103-12 investment entities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	36.5	30.2
Level 1 [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	106.6	84.3
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	79.2	62.7
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	25.5	19.5
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	1.9	2.1
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	441.8	339.6
Level 2 [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1.9	1.9
Level 2 [Member] | U.S. government securities [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2.0	3.1
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	20.8	3.0
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	185.9	145.8
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	37.3	28.2
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	60.1	43.0
Level 2 [Member] | Corporate debt commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	72.8	65.7
Level 2 [Member] | Inflation protection commingled funds [Member]
Defined Benefit Plan Disclosure Fair Value [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	24.5	18.7
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	$ 36.5	$ 30.2