Stockholders' Equity (Details) (USD $)	3 Months Ended								12 Months Ended			3 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015		Dec. 31, 2013
Dividends Per Share, Common Stock	$ 0.82		$ 0.35		$ 0.35		$ 0.35
Dividends Per Share, Convertible Preferred Stock	$ 1.1250		$ 1.1250		$ 1.1250		$ 1.1625
Aggregate Payment Amount, Common Stock	$ 274,500,000	[1],[2]	$ 117,200,000	[1],[2]	$ 117,200,000	[1],[2]	$ 117,200,000	[1],[2]	$ 626,074,000
Aggregate Payment Amount, Convertible Preferred Stock	11,000,000		11,000,000		11,000,000		11,400,000
Proceeds from Issuance of Common Stock										2,980,586,000
4.5% Mandatory Convertible Preferred Stock, Par or Stated Value Per Share	$ 0.01								$ 0.01	$ 0.01				0.01
Net proceeds from issuance of preferred stock									0	950,886,000	0
Purchases of common stock, value									21,800,000	99,500,000	36,000,000
Common Stock
Declaration Date	Oct. 30, 2014		Aug. 08, 2014		May 30, 2014		Feb. 20, 2014
Record Date	Dec. 19, 2014		Sep. 19, 2014		Jun. 20, 2014		Mar. 20, 2014
Payment Date	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014
Stock Issued During Period, Shares, New Issues										41,400,000
Proceeds from Issuance of Common Stock										414,000
Purchases of common stock, shares									(292,874)	(1,429,461)	(700,070)
4.5% Mandatory Convertible Preferred Stock
Stock Issued During Period, Shares, New Issues										9,775,000
Net proceeds from issuance of preferred stock										98,000
Convertible Preferred Stock [Member]
Declaration Date	Dec. 22, 2014		Sep. 26, 2014		Jun. 25, 2014		Mar. 25, 2014							Dec. 31, 2013
Record Date	Oct. 15, 2014		Jul. 15, 2014		Apr. 15, 2014		Jan. 15, 2014					Jan. 15, 2015
Payment Date	Nov. 03, 2014		Aug. 01, 2014		May 01, 2014		Feb. 03, 2014
Minimum [Member]
Conversion factor, Preferred Stock									1.1080
Maximum [Member]
Conversion factor, Preferred Stock									1.3850
Paid subsequent to year end [Member]
Dividends Per Share, Convertible Preferred Stock												1.1250
Aggregate Payment Amount, Convertible Preferred Stock												11,000,000	[3]
Paid subsequent to year end [Member] | Convertible Preferred Stock [Member]
Payment Date												Feb. 02, 2015

[1] The Company's common stock dividends are considered ordinary in nature for income tax purposes.

[2] Inclusive of dividends accrued for holders of RSUs.

[3] Represents amount paid on February 2, 2015 based on holders of record on January 15, 2015.