Shareholders' Equity - Common Share Rollforward (Details) - USD ($) $ / shares in Units, $ in Millions												12 Months Ended
	Dec. 19, 2019	Aug. 06, 2019	Jun. 19, 2019	Jun. 04, 2019	Apr. 09, 2019	Apr. 04, 2019	Jan. 03, 2019	Mar. 26, 2018	Dec. 26, 2017	Apr. 12, 2017	Mar. 09, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 11, 2019	Sep. 12, 2018
Increase (Decrease) in Stockholders' Equity
Common stock, shares issued, beginning balance (in shares)												272,431,745
Common stock, shares outstanding, beginning balance (in shares)												150,978,184	172,000,000.0	194,600,000
Common stock, shares issued (in shares)												(100,000)		0
Common stock, shares acquired under share repurchase (in shares)	2,591,093	695,566	2,963,512	879,199	3,593,453	290,765	5,059,449	1,947,413	7,821,666	3,986,647	0	21,100,000	(22,800,000)	24,400,000
Common stock, shares issued for share-based compensation programs (in shares)												2,300,000	1,800,000	1,800,000
Treasury Stock retirement (in shares)												0
Common stock, shares issued, ending balance (in shares)												140,726,677	272,431,745
Common stock, shares outstanding, ending balance (in shares)												132,325,790	150,978,184	172,000,000.0
Dividends declared per share of Common Stock (in dollars per share)												$ 0.32	$ 0.04	$ 0.04
Payment	$ 200		$ 200		$ 236		$ 250		$ 500		$ 150	$ 1,136	$ 1,025	$ 923
Total Shares Repurchased (in shares)		3,659,078		4,472,652		5,350,214		9,769,079		3,986,647
Preferred Stock
Increase (Decrease) in Stockholders' Equity
Payment												$ 0	$ 0	$ 0
Preferred stock, shares issued (in shares)												625,000	325,000
Preferred stock, shares outstanding (in shares)												625,000	325,000
Common Stock
Increase (Decrease) in Stockholders' Equity
Common stock, shares issued, beginning balance (in shares)												272,400,000	270,000,000.0	268,000,000.0
Common stock, shares issued (in shares)												(100,000)	0	0
Common stock, shares acquired under share repurchase (in shares)												0	0	0
Common stock, shares issued for share-based compensation programs (in shares)												3,200,000	2,400,000	2,000,000.0
Treasury Stock retirement (in shares)												(135,000,000.0)
Common stock, shares issued, ending balance (in shares)												140,700,000	272,400,000	270,000,000.0
Payment												$ 0	$ 0	$ 0
Treasury Stock
Increase (Decrease) in Stockholders' Equity
Common stock, shares held in treasury, beginning balance (in shares)												(121,400,000)	(98,000,000.0)	(73,400,000)
Common stock, shares issued (in shares)												0	0	0
Common stock, shares acquired under share repurchase (in shares)												21,100,000	(22,800,000)	24,400,000
Common stock, shares issued for share-based compensation programs (in shares)												900,000	(600,000)	200,000
Treasury Stock retirement (in shares)												(135,000,000.0)
Common stock, shares held in treasury, ending balance (in shares)												(8,400,000)	(121,400,000)	(98,000,000.0)
Payment												$ 1,096	$ 1,125	$ 1,023
Series A Preferred Stock
Increase (Decrease) in Stockholders' Equity
Preferred stock, shares issued (in shares)												325,000	325,000			325,000
Preferred stock, shares outstanding (in shares)												325,000	325,000
Series B Preferred Stock
Increase (Decrease) in Stockholders' Equity
Preferred stock, shares issued (in shares)												300,000	0		300,000
Preferred stock, shares outstanding (in shares)												300,000	0