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Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
4.0% Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, repayments (in dollars)		$ 105
Debt instrument, convertible, conversion price (in dollars per share)		$ 15.76
4.25% Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, repayments (in dollars)	$ 97
Debt instrument, convertible, conversion price (in dollars per share)	$ 15.48			$ 15.48
4.25% Convertible Notes Issued in 2011 [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, conversion price (in dollars per share)	15.48			15.48
4.25% Convertible Notes Issued in 2009 [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, conversion price (in dollars per share)	$ 15.48			$ 15.48
4.0% Convertible Notes Issued in 2011 [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, conversion price (in dollars per share)		15.76
4.0% Convertible Notes Issued in 2009 [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, conversion price (in dollars per share)		$ 15.76
Convertible Debt [Member]
Earnings Per Share [Line Items]
Premium shares (in shares)			0	5,430,000	7,201,000
Convertible Debt [Member] \| 2011 Convertible Notes [Member]
Earnings Per Share [Line Items]
Premium shares (in shares)				5,000,000
Convertible Debt [Member] \| 4.0% Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, matured and converted (in dollars)		$ 115
Debt instrument, convertible, interest rate (percentage)		4.00%
Convertible Debt [Member] \| 4.25% Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, matured and converted (in dollars)	$ 100
Debt instrument, convertible, interest rate (percentage)	4.25%			4.25%
Convertible Debt [Member] \| 2009 Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, matured and converted (in dollars)				$ 13
Convertible Debt [Member] \| 2011 Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, matured and converted (in dollars)				$ 202
Common Stock [Member]
Earnings Per Share [Line Items]
Weighted average anti-dilutive common stock equivalents (in shares)			563,803	244,623	0
Common Stock [Member] \| 2011 Convertible Notes [Member]
Earnings Per Share [Line Items]
Number of conversion shares, principal amount (in shares)				13,000,000
Common Stock [Member] \| 4.0% Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, common shares issued (in shares)		4,200,000
Common Stock [Member] \| 4.25% Convertible Notes [Member]
Earnings Per Share [Line Items]
Debt instrument, convertible, common shares issued (in shares)	2,400,000
Common Stock [Member] \| Convertible Debt [Member] \| 2011 Convertible Notes [Member]
Earnings Per Share [Line Items]
Premium shares (in shares)					6,400,000
Common Stock [Member] \| Common Stock Equivalents Excluded Due To Net Loss [Member]
Earnings Per Share [Line Items]
Weighted average anti-dilutive common stock equivalents (in shares)			563,803