Share-Based Incentive Compensation (details) - Summary of Restricted and Deferred Stock Units and Performance Share Activity (USD $)	12 Months Ended
	Dec. 31, 2012
Restricted and deferred stock units [Member]
Summary of other equity instruments [Roll Forward]
Other equity instruments, outstanding, number, beginning of year	2,780,504
Other equity instruments, granted, number	953,630
Other equity instruments, vested, number	(1,379,608)
Other equity instruments, forfeited, number	(158,144)
Other equity instruments, outstanding, number, end of year	2,196,382
Other equity instruments, outstanding, weighted average grant-date fair value, beginning of year	$ 48.03
Other equity instruments, granted, weighted average grant-date fair value	$ 60.18
Other equity instruments, vested, weighted average grant-date fair value	$ 42.90
Other equity instruments, forfeited, weighted average grant-date fair value	$ 52.96
Other equity instruments, outstanding, weighted average grant-date fair value, end of year	$ 56.17
Term of share-based compensation awards	These restricted stock unit awards are granted at market price, generally vest three years from the date of grant, do not have voting rights and the underlying shares of common stock are not issued until the vesting criteria is satisfied.
Performance shares [Member]
Summary of other equity instruments [Roll Forward]
Other equity instruments, outstanding, number, beginning of year	1,547,402
Other equity instruments, granted, number	719,841
Other equity instruments, vested, number	(868,250)
Other equity instruments, forfeited, number	(70,856)
Other equity instruments, performance-based adjustment, number	110,084
Other equity instruments, outstanding, number, end of year	1,438,221
Other equity instruments, outstanding, weighted average grant-date fair value, beginning of year	$ 53.79
Other equity instruments, granted, weighted average grant-date fair value	$ 59.48
Other equity instruments, vested, weighted average grant-date fair value	$ 51.82
Other equity instruments, forfeited, weighted average grant-date fair value	$ 55.15
Other equity instruments, performance-based adjustment, weighted average grant-date fair value	$ 54.06
Other equity instruments, outstanding, weighted average grant-date fair value, end of year	$ 58.22
Term of share-based compensation awards	The performance awards provide the recipient the right to earn shares of the Company's common stock based upon the Company's attainment of certain performance goals. The performance goals for performance awards are based on the Company's adjusted return on equity over a three-year performance period. Vesting of any performance shares is contingent upon the Company attaining the relevant performance period minimum threshold return on equity. If the performance period return on equity is below the minimum threshold, none of the shares will vest. If performance meets or exceeds the minimum performance threshold, a range of performance shares will vest (50%-160% for awards granted prior to and including February 2009; 50%-150% for awards granted in February 2010; and 50%-130% for awards granted in February 2011, 2012 and 2013; depending on the actual return on equity attained.
Performance shares granted in February 2009 and prior [Member] | Minimum [Member]
Summary of other equity instruments [Roll Forward]
Performance threshold	50.00%
Performance shares granted in February 2009 and prior [Member] | Maximum [Member]
Summary of other equity instruments [Roll Forward]
Performance threshold	160.00%
Performance shares granted in February 2010 [Member] | Minimum [Member]
Summary of other equity instruments [Roll Forward]
Performance threshold	50.00%
Performance shares granted in February 2010 [Member] | Maximum [Member]
Summary of other equity instruments [Roll Forward]
Performance threshold	150.00%
Performance shares granted in February 2011, 2012 and 2013 [Member] | Minimum [Member]
Summary of other equity instruments [Roll Forward]
Performance threshold	50.00%
Performance shares granted in February 2011, 2012 and 2013 [Member] | Maximum [Member]
Summary of other equity instruments [Roll Forward]
Performance threshold	130.00%