Pension, Postretirement, Other Postemployment, and Employee Savings Plan Benefits (Details 6) (USD $) In Millions, unless otherwise specified									12 Months Ended
	Dec. 31, 2011 Pension Plan	Dec. 31, 2010 Pension Plan	Dec. 31, 2009 Pension Plan	Dec. 31, 2011 Qualified Pension Plans	Dec. 31, 2011 Level 1 Qualified Pension Plans	Dec. 31, 2010 Level 1 Qualified Pension Plans	Dec. 31, 2011 Level 2 Qualified Pension Plans	Dec. 31, 2010 Level 2 Qualified Pension Plans	Dec. 31, 2011 Level 3 Qualified Pension Plans	Dec. 31, 2010 Level 3 Qualified Pension Plans	Dec. 31, 2011 Alternative investments Qualified Pension Plans	Dec. 31, 2010 Alternative investments Qualified Pension Plans	Dec. 31, 2011 Alternative investments Level 3 Qualified Pension Plans	Dec. 31, 2010 Alternative investments Level 3 Qualified Pension Plans	Dec. 31, 2011 Cash and cash equivalents Qualified Pension Plans	Dec. 31, 2010 Cash and cash equivalents Qualified Pension Plans	Dec. 31, 2011 Cash and cash equivalents Level 1 Qualified Pension Plans	Dec. 31, 2010 Cash and cash equivalents Level 1 Qualified Pension Plans
Change in plan assets
Fair value of plan assets at beginning of period	$ 1,487.7	$ 1,408.1	$ 1,058.1	$ 1,487.7	$ 226.1	$ 277.8	$ 1,098.9	$ 1,012.0	$ 118.3	$ 74.4	$ 118.3	$ 74.4	$ 162.7	$ 118.3	$ 49.0	$ 93.6	$ 49.0	$ 93.6
Actual return on plan assets:
Assets still held at year end									(11.1)	(32.1)	(11.1)	(32.1)
Assets sold during the year									7.4	37.0	7.4	37.0
Purchases									160.3
Sales									(112.2)
Net purchases, sales and settlements									48.1	22.2	48.1	22.2
Transfers into Level 3										16.8		16.8
Net transfers into and out of Level 3											0
Fair value of plan assets at end of period	$ 1,487.7	$ 1,408.1	$ 1,058.1	$ 1,487.7	$ 226.1	$ 277.8	$ 1,098.9	$ 1,012.0	$ 162.7	$ 118.3	$ 162.7	$ 118.3	$ 162.7	$ 118.3	$ 49.0	$ 93.6	$ 49.0	$ 93.6