Shareholders' Equity - Shares Repurchased (Details) - USD ($)	1 Months Ended	3 Months Ended							9 Months Ended		10 Months Ended	12 Months Ended
	Nov. 05, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Nov. 05, 2020	Dec. 31, 2019	Nov. 02, 2020
Equity, Class of Treasury Stock [Line Items]
Repurchases of common stock									$ 320,000,000	$ 340,000,000
Common Shares
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares)		1,857,323	5,956,422	3,629,410	3,335,517	3,400,677	2,519,130	1,908,605				11,163,929
Repurchases of common stock		$ 40,000,000	$ 164,000,000	$ 116,000,000	$ 160,000,000	$ 150,000,000	$ 111,000,000	$ 79,000,000				$ 500,000,000
Average price paid per share (in dollars per share)		$ 21.72	$ 27.49	$ 32.03	$ 47.97	$ 44.11	$ 43.89	$ 41.62				$ 44.79
Subsequent Event | Common Shares
Equity, Class of Treasury Stock [Line Items]
Repurchase authorized amount													$ 250,000,000
Remaining capacity of shares repurchase program	$ 332,000,000										$ 332,000,000
Shares repurchased (in shares)	1,726,524										13,169,679
Repurchases of common stock	$ 46,000,000										$ 366,000,000
Average price paid per share (in dollars per share)	$ 26.36										$ 27.78