Stock Incentive Plans - Performance Share Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Share Plan Expense, Liability Portion			$ 19.6		$ 16.6
Incremental modification expense	7.0
Performance Share Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awarding of performance shares earned payable in cash	40.00%
Awarding of performance shares earned payable in common stock	60.00%
Compensation expense recognized in cash by Company over the performance period	40.00%
Compensation expense recognized in common stock by Company over the performance period	60.00%
Performance share plan expense	$ 35.5		$ 26.3		$ 23.9
Performance share plan, shares issued in period	558,000	[1]	538,180	[1]	104,205	[1]

[1] Shares are issued in February of the following year.