Shareholders' Equity - Narrative (Details) - USD ($)											2 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 27, 2019	Aug. 06, 2019	Jun. 19, 2019	Jun. 11, 2019	Jun. 04, 2019	Apr. 09, 2019	Apr. 04, 2019	Jan. 03, 2019	Sep. 12, 2018	May 07, 2013	Aug. 06, 2019	Jun. 04, 2019	Sep. 30, 2019	Apr. 04, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Oct. 31, 2019	May 02, 2019
Class of Stock [Line Items]
Dividends declared per share of Common Stock (usd per share)													$ 0.15		$ 0.01	$ 0.17	$ 0.03
Amount authorized for repurchase																				$ 500,000,000
Payment for share repurchases			$ 200,000,000			$ 236,000,000		$ 250,000,000					$ 250,000,000		$ 250,000,000	$ 936,000,000	$ 750,000,000
Shares delivered (in shares)		695,566	2,963,512		879,199	3,593,453	290,765	5,059,449			3,659,078	4,472,652		5,350,214		(18,500,000)		(22,800,000)
Number of warrants issued and outstanding (in shares)										26,050,846
Warrants issued allowing purchase of shares, percentage of common stock issued and outstanding										9.99%
Exercise price of warrants (usd per share)	$ 48.61									$ 48.75
Number of shares of common stock for which each warrant is exercisable (in shares)	1.002840621
Cash dividends, per share (usd per share)	$ 0.15									$ 0.01
Warrants net share settled, fair value										$ 94,000,000
Number of warrants exercised													0			0
Preferred Stock, par value per share													$ 0.01			$ 0.01		$ 0.01
Proceeds from issuance of preferred stock, net																$ 293,000,000	$ 319,000,000
Issuer's redemption option, period to redeem after a redemption event																90 days
Preferred Stock, shares authorized													100,000,000			100,000,000		100,000,000
Preferred Stock, amount of preferred dividends in arrears																$ 0
Subsequent Event
Class of Stock [Line Items]
Amount authorized for repurchase																			$ 800,000,000
Rating agency event
Class of Stock [Line Items]
Preferred stock, redemption price per share													$ 1,020			$ 1,020
Regulatory capital event
Class of Stock [Line Items]
Preferred stock, redemption price per share													$ 1,000			$ 1,000
Series A Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares issued									325,000				325,000			325,000		325,000
Preferred Stock, shares outstanding													325,000			325,000		325,000
Preferred Stock, dividend rate, percentage									6.125%
Preferred Stock, par value per share									$ 0.01
Preferred stock, liquidation preference per share									$ 1,000
Proceeds from issuance of preferred stock, net									$ 319,000,000
Series B Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares issued				300,000									300,000			300,000		0
Preferred Stock, shares outstanding													300,000			300,000		0
Preferred Stock, dividend rate, percentage				5.35%
Preferred Stock, par value per share				$ 0.01
Preferred stock, liquidation preference per share				$ 1,000
Proceeds from issuance of preferred stock, net				$ 293,000,000
Number of shares of preferred stock represented by each depositary share (in shares)													0.025			0.025
Depositary Shares | Rating agency event
Class of Stock [Line Items]
Preferred stock, redemption price per share													$ 25.50			$ 25.50
Depositary Shares | Regulatory capital event
Class of Stock [Line Items]
Preferred stock, redemption price per share													$ 25.00			$ 25.00
Open market repurchase
Class of Stock [Line Items]
Payment for share repurchases																$ 250,000,000
Shares delivered (in shares)																4,926,775