Common Stock - Summary of Nonvested Restrict Stock Unit Activity (Details) (Restricted Stock [Member], USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2014
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested at December 31, 2013	3,386,697	[1]
Granted	2,252,574
Vested	(1,216,016)
Forfeited	(86,094)
Undistributed vested awards	(578,943)	[2]
Nonvested at December 31, 2014	3,758,218	[1]	3,386,697	[1]
Nonvested, Weighted Average Exercise Price (in usd per share)	$ 34.10	[1]				$ 31.27	[1]
Granted, Weighted Average Grant Date Fair Value (in usd per share)	$ 28.71		$ 31.06		$ 39.94
Vested, Weighted Average Exercise Price (in usd per share)	$ 35.36
Forfeited, Weighted Average Exercise Price (in usd per share)	$ 31.99
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	$ 29.17	[2]
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees	975,116		931,628

[1] Excludes 975,116 and 931,628 of restricted stock units issued to retirement-eligible employees as of December 31, 2014 and December 31, 2013, respectively, as they are fully vested.

[2] Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2014.