Changes in Capital Structure Changes in Capital Structure (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended						0 Months Ended		9 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2014 Common Class A	Dec. 31, 2013 Common Class A	Jul. 29, 2014 Public Shareholders Common Class A	Jul. 22, 2013 Public Shareholders Common Class A	Sep. 30, 2014 Public Shareholders Common Class A	Sep. 30, 2013 Public Shareholders Common Class A
Class of Stock [Line Items]
Common Stock, Shares, Outstanding					34,586,250	22,511,250
Dividends		$ 0.375
Sale of Stock, Number of Shares Issued in Transaction							12,075,000	22,511,250
Proceeds from Issuance of Common Stock							$ 630		$ 630	$ 468
Dividends Payable, Date to be Paid	Dec. 15, 2014	Sep. 15, 2014	Jun. 16, 2014	Mar. 17, 2014