Consolidated Balance Sheets (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Accounts receivable - trade, allowance for doubtful accounts (in millions)	23,000,000		40,000,000
Intangible assets, accumulated amortization (in millions)	1,402,000,000	[1]	1,977,000,000	[1]
3.625% convertible perpetual preferred stock, par value (in dollars)	0.01		0.01
3.625% convertible perpetual preferred stock, shares issued	250,000		250,000
3.625% convertible perpetual preferred stock, shares outstanding	250,000		250,000
3.625% convertible perpetual preferred stock, liquidation value (in dollars)	250		250
Common stock, par value (in dollars)	0.01		0.01
Common stock, shares authorized	500,000,000		500,000,000
Common stock, shares issued	415,506,176		401,126,780
Common stock, shares outstanding	336,662,624		323,779,252
Treasury stock, shares	78,843,552		77,347,528
Convertible Preferred Stock [Member]
Preferred Stock, Dividend Rate Amended, Percentage	2.822%
3.625% convertible perpetual preferred stock, interest rate (as a percent)	3.625%		3.625%

[1] Adjusted for write-off of fully amortized customer contracts of $843 million.