Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock dividends declared and paid			$ 800	$ 400	$ 375
Preferred stock par value (in dollars per share)			$ 0.01	$ 0.01
Proceeds from issuance of preferred stock			$ 492	$ 0	492
Fixed-to-Floating Rate Cumulative Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Dividends paid			$ 58	$ 58	$ 59
Preferred stock shares issued			1,000,000	1,000,000
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [Member]
Class of Stock [Line Items]
Dividends paid			$ 32	$ 33
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%
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series C [Member]
Class of Stock [Line Items]
Preferred stock shares issued			500,000	0
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	5.70%
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series C [Member] | US Treasury Interest Rate [Member]
Class of Stock [Line Items]
Variable dividend payment rate	4.997