Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions			9 Months Ended
	Oct. 26, 2018	Sep. 24, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock par value (in dollars per share)			$ 0.01		$ 0.01
Proceeds from issuance of preferred stock			$ 492	$ 985
Subsequent Event [Member]
Class of Stock [Line Items]
Common stock dividends declared	$ 375
Preferred Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Amount set aside to pay dividends	$ 46
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock shares issued					1,000,000
Preferred stock dividend rate			5.75%
Preferred stock dividends paid			$ 59
Series A Preferred Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 28.75
Preferred stock dividends declared	$ 29
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [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		6.50%
Fixed-to-Floating Rate Cumulative Perpetual Preferred Stock, Series B [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
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%