Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock dividends declared and paid	$ 400	$ 375
Preferred stock dividends declared					$ 45	$ 46
Preferred stock par value (in dollars per share)					$ 0.01	$ 0.01
Proceeds from issuance of preferred stock					$ 0	$ 492	$ 985
Fixed-to-Floating Rate Cumulative Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Dividends paid					$ 58	$ 59
Preferred stock dividends declared	$ 29
Preferred stock dividends declared (in dollars per share)	$ 28.75
Preferred stock shares issued				1,000,000	1,000,000	1,000,000
Preferred stock par value (in dollars per share)				$ 0.01
Liquidation preference (in dollars per share)				$ 1,000
Proceeds from issuance of preferred stock				$ 985
Preferred stock dividend rate				5.75%
Fixed-to-Floating Rate Cumulative Preferred Stock, Series A [Member] | LIBOR [Member]
Class of Stock [Line Items]
Preferred stock floating rate				3.598%
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [Member]
Class of Stock [Line Items]
Dividends paid					$ 33
Preferred stock dividends declared	$ 16
Preferred stock dividends declared (in dollars per share)	$ 32.5
Preferred stock shares issued			500,000		500,000	500,000
Preferred stock par value (in dollars per share)			$ 0.01
Liquidation preference (in dollars per share)			$ 1,000
Proceeds from issuance of preferred stock			$ 492
Preferred stock dividend rate					6.50%
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [Member] | LIBOR [Member]
Class of Stock [Line Items]
Preferred stock floating rate					3.436%
Dividend Declared [Member]
Class of Stock [Line Items]
Amount set aside to pay dividends	$ 45