Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended	3 Months Ended					12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2008	Mar. 31, 2012 Stock Options And Stock-Settled SARS [Member]	Mar. 31, 2011 Stock Options And Stock-Settled SARS [Member]	Mar. 31, 2012 Cash-Settled SARS [Member]	Mar. 31, 2011 Cash-Settled SARS [Member]	Dec. 31, 2011 Cash-Settled SARS [Member]	Dec. 31, 2010 Performance Stock [Member]	Dec. 31, 2008 Performance Stock [Member]	Mar. 31, 2012 1993 Plan [Member]	Dec. 31, 2011 1993 Plan [Member]	Mar. 31, 2012 Amendment 1993 Plan [Member]	Mar. 31, 2012 Non-Vested Stock, Non-Vested Stock Units And Performance Stock [Member]	Mar. 31, 2011 Non-Vested Stock, Non-Vested Stock Units And Performance Stock [Member]	Mar. 31, 2012 Non-Vested Stock, Non-Vested Stock Units And Performance Stock [Member] Non-Vested Stock And Non-Vested Stock Units [Member]	Mar. 31, 2012 Non-Vested Stock, Non-Vested Stock Units And Performance Stock [Member] Non-Vested Stock Units [Member]
Share-Based Compensation Arrangement By Share-Based Payment Award [Line Items]
Shares reserved for issuance											6,600,000
Increase in number of shares issuable under the plan													2,000,000
Shares reserved for issuance for all outstanding share-based compensation grants											3,800,000
Stock option grant component, percentage of market price				100.00%
Contractual life (years)				10 years
Stock awards granted	470,809			470,809						47,927
Weighted-average grant-date fair value	$ 19.91	$ 20.83		$ 19.91	$ 20.83
Total intrinsic value of stock options and stock-settled SARS exercised				$ 12.1	$ 3.0
Total fair value of stock options and stock-settled SARS vested				6.5	6.6
Total unrecognized compensation cost				13.5												5.3
Weighted-average period to recognize total unrecognized compensation cost (years)				1.4												1.8
Vesting period for majority of awards (years)				3 years
Intrinsic value and cash used to settle exercises of cash-settled SARS						0.2	0.1
Tax benefits realized				3.0	1.1
Cash received from stock options exercised	13.4	3.3		13.4	3.3
Weighted average fair value of the non-vested stock and non-vested stock per share																$ 48.82
Pre-tax compensation cost related to stock option and stock-settled SARS				2.1	1.9
Pre-tax expense (income) recognized for cash-settled SARS						0.9	(0.3)
Liability related to cash-settled SARS						2.0		1.3
Non-vested stock and stock units grants	67,139																67,139
Performance stock awards, vested									8,092
Performance stock awards recorded as expense									0.4
Compensation cost recognized											0.5	0.3		0.9	0.6
Additional paid-in capital representing excess tax benefits available to absorb potential future tax deficiencies											$ 74.0	$ 71.7
Share-based compensation, share grants in period, number of employees			9