Employee Benefit Plans (Details 3) (Significant Unobservable Inputs (Level 3), USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Changes in the fair value of Level 3 assets
Fair value of plan assets - beginning of year	$ 161.7	$ 131.9
Realized gains	0.1	1.3
Unrealized gains (losses) relating to instruments still held at period end	16.5	13.9
Purchases	15.8	24.3
Sales	(0.7)	(9.7)
Fair value of plan assets - end of year	193.4	161.7
Global Equity Common Trust Funds
Changes in the fair value of Level 3 assets
Fair value of plan assets - beginning of year	24.4
Unrealized gains (losses) relating to instruments still held at period end	1.8	1.6
Purchases	2.8	24.3
Sales		(1.5)
Fair value of plan assets - end of year	29.0	24.4
Commingled Global Fund Allocations
Changes in the fair value of Level 3 assets
Fair value of plan assets - beginning of year	129.9	122.4
Realized gains		0.7
Unrealized gains (losses) relating to instruments still held at period end	12.7	13.1
Purchases	13.0
Sales		(6.3)
Fair value of plan assets - end of year	155.6	129.9
Fixed Income Common Trust Funds
Changes in the fair value of Level 3 assets
Fair value of plan assets - beginning of year		1.3
Unrealized gains (losses) relating to instruments still held at period end		0.1
Fair value of plan assets - end of year	1.4	1.4
Other
Changes in the fair value of Level 3 assets
Fair value of plan assets - beginning of year	6.0	8.2
Realized gains	0.1	0.6
Unrealized gains (losses) relating to instruments still held at period end	2.0	(0.9)
Sales	(0.7)	(1.9)
Fair value of plan assets - end of year	$ 7.4	$ 6.0