Common Stockholders' Equity and Preferred Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Number of shares repurchased (in shares)	17,500,000
Repurchases of common stock	$ 1,250,000,000	$ 1,844,000,000	$ 2,607,000,000
Share repurchase program additional amount authorized		$ 3,000,000,000.0
Amount remaining under repurchase programs	$ 1,800,000,000
Common stock reserved for future issuance (in shares)	10,000,000
Junior preferred stock outstanding (in shares)	2
Junior preferred stock par value per share (in dollars per share)	$ 0.01
Preferred stock authorized to issue (in shares)	250,000,000