Preferred Stock (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) Days $ / shares shares	Dec. 31, 2014 USD ($)	[1]	Dec. 31, 2013 USD ($)	[1]
Equity [Abstract]
Preferred stock, ACS acquisition shares issued | shares	300,000
ACS acquisition, Series A convertible preferred stock aggregate liquidation preference | $	$ 300,000,000
Preferred stock aggregate fair value | $	$ 349,000,000
Preferred stock, dividend rate, percentage	8.00%
Cash dividends declared-preferred stock | $	$ 24,000,000	$ 24,000,000		$ 24,000,000
Preferred stock converted into common shares | shares	89.8876
Total conversion of number of preferred stock shares into common stock, shares | shares	26,966,000
Total conversion of preferred stock shares into common stock, initial conversion price per share | $ / shares	$ 11.125
Common stock closing price, maximum threshold, triggering conversion of Pfd to Common Stock	130.00%
Minimum number of trading days C/S close price must exceed conversion price to trigger Pfd Stock conversion | Days	20
Number of trading days used for measurement | Days	30

[1] Cash dividends declared on preferred stock of $20 per share in each quarter of 2015, 2014 and 2013.