Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Equity:
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	200,000,000	200,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock
Equity:
Common stock, par value (usd per share)		$ 0.01
Common stock, shares authorized		1,000,000,000
Common stock, shares issued		228,491,312
Common stock, shares outstanding		228,491,312
Class A
Equity:
Common stock, par value (usd per share)	$ 0.01
Common stock, shares authorized	700,000,000
Common stock, shares issued	100,086,387
Common stock, shares outstanding	100,086,387
Class B
Equity:
Common stock, par value (usd per share)	$ 0.01
Common stock, shares authorized	300,000,000
Common stock, shares issued	114,566,254
Common stock, shares outstanding	114,566,254