Stockholders' Equity Conversion Rights (Details) (USD $)	5 Months Ended	48 Months Ended	12 Months Ended
	Dec. 31, 2011	Feb. 10, 2019	Dec. 31, 2014 votes	Feb. 10, 2015
Class of Stock [Line Items]
Stock repurchased during period, shares	7,500,000
Stock repurchased during period, value	$ 321,100,000
Subsequent event
Class of Stock [Line Items]
Common stock repurchase program, expected term		4 years
Class B exchangeable shares
Class of Stock [Line Items]
Common stock, votes per share			1
Exchangeable shares issued, Class A
Class of Stock [Line Items]
Common stock, votes per share			1
Common stock, conversion ratio			1
Class A and Class B common stock
Class of Stock [Line Items]
Stock repurchase program, authorized amount	1,200,000,000.0
Class A and Class B common stock | Subsequent event
Class of Stock [Line Items]
Stock repurchase program, authorized amount				$ 1,000,000,000