Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended			12 Months Ended
	Sep. 24, 2018	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2017
Class of Stock [Line Items]
Common stock dividends declared and paid		$ 375
Preferred stock par value (in dollars per share)					$ 0.01	$ 0.01
Common stock par value per share (in usd per share)				$ 0.0001	$ 0.0001	$ 0.0001		$ 1
Proceeds from issuance of preferred stock					$ 492	$ 985	$ 0
Preferred stock dividends declared					46
Issuance of preferred stock					492	$ 985
Common Stock [Member]
Class of Stock [Line Items]
Stock split conversion ratio				10,000
Preferred Stock [Member]
Class of Stock [Line Items]
Amount set aside to pay dividends		$ 46
Fixed-to-Floating Rate Cumulative Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Preferred stock par value (in dollars per share)				$ 0.01
Preferred stock shares issued						1,000,000
Liquidation preference (in dollars per share)				$ 1,000
Preferred stock dividend rate				5.75%
Preferred stock dividends paid					$ 59
Preferred stock dividends declared (in dollars per share)		$ 28.75
Preferred stock dividends declared		$ 29
Stock issued during period (shares)				1,000,000
Issuance of preferred stock				$ 985
Fixed-to-Floating Rate Cumulative Preferred Stock, Series A [Member] | LIBOR [Member]
Class of Stock [Line Items]
Preferred stock variable dividend rate				3.598%
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [Member]
Class of Stock [Line Items]
Preferred stock par value (in dollars per share)			$ 0.01
Preferred stock shares issued			500,000		500,000	0
Liquidation preference (in dollars per share)			$ 1,000
Proceeds from issuance of preferred stock			$ 492
Preferred stock dividend rate	6.50%
Preferred stock dividends declared (in dollars per share)		$ 33.58
Preferred stock dividends declared		$ 17
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [Member] | LIBOR [Member]
Class of Stock [Line Items]
Preferred stock floating rate	3.436%