Incentive Plans and Deferred Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended								12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2011 Annual incentive plan Y	Dec. 31, 2010 Annual incentive plan	Dec. 31, 2009 Annual incentive plan	Dec. 31, 2011 Long-term incentive plan Y	Dec. 31, 2010 Long-term incentive plan	Dec. 31, 2009 Long-term incentive plan	Dec. 31, 2011 Long-term incentive plan Class A	Sep. 30, 2011 Long-term incentive plan 2009-2011 performance period	Dec. 31, 2010 Long-term incentive plan 2008-2010 performance period	Jul. 31, 2011 Long-term incentive plan 2008-2010 performance period	Dec. 31, 2009 Long-term incentive plan 2007-2009 performance period	Jul. 31, 2010 Long-term incentive plan 2007-2009 performance period	Dec. 31, 2011 Deferred compensation plans	Dec. 31, 2010 Deferred compensation plans	Dec. 31, 2009 Deferred compensation plans	Dec. 31, 2011 Annual incentive, long-term incentive and deferred compensation plans	Dec. 31, 2010 Annual incentive, long-term incentive and deferred compensation plans	Dec. 31, 2009 Annual incentive, long-term incentive and deferred compensation plans	Dec. 31, 2011 Stock compensation plan for outside directors Class A	Dec. 31, 2010 Stock compensation plan for outside directors Class A	Dec. 31, 2009 Stock compensation plan for outside directors Class A
Incentive plans and deferred compensation
Performance period of incentive plans (in years)	1			3
Compensation cost charged to operations, after-tax, cash based	$ 2.0	$ 3.0	$ 2.0
Compensation cost charged to operations, after-tax, share based				6.0	4.0	2.0
Average share price (in dollars per share)									$ 73.97		$ 44.48
Maximum number of shares that may be issued pursuant to awards granted (in shares)							1,000,000
Maximum number of shares which may be earned in each performance period by any single participant (in shares)							250,000
Maximum dollar amount which may be earned in each performance period by any single participant				3
Awards, employer match and hypothetical earnings by plan:
Long-term incentive plan awards				9	7	4
Annual incentive plan awards	3	4	3
Deferred compensation plans, employer match and hypothetical earnings													1	2	1
Total plan awards and earnings																13	13	8
Total plan awards paid, share based										5		2
Estimated plan award								5
Total plan awards paid, cash and/or share based																(10)	(6)	(8)
Compensation deferred under the plans													0	1	1
Distributions from the deferred compensation plans													(1)	(1)	(1)
Gross incentive plan and deferred compensation liabilities at end of period																24	22	15
Vesting terms under stock compensation plan for outside directors																			Each director vests in the grant 25% every three months over the course of a year
Annual charge related to stock compensation plan for outside directors																			$ 1.0	$ 2.0	$ 0.4