Stock-Based Compensation (Summary of Restricted Stock Award Activity) (Details) (Restricted Stock Awards [Member], USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding at the beginning of the year, number of shares	3,403
Shares granted, number of shares	836	[1]
Shares vested, number of shares	(1,942)	[2]
Shares forfeited, number of shares	(8)
Shares outstanding at the end of the period, number of shares	2,289
Shares granted, weighted-average grant-date fair value	$ 38.28
Weighted-average requisite service period (years)	2.5Y
Expected volatility rate on restricted stock awards	31.00%
Fair value of shares on vesting date	$ 99.7

[1] Weighted-average grant-date fair value of $38.28 per share and a weighted-average requisite service period of 2.5 years. The awards with market conditions included an expected volatility of 31% in the Monte Carlo simulation used to measure grant-date fair value.

[2] Fair value on vesting date of $99.7 million.