Stockholders' Equity - Common Stock Dividends and Reconciliation of Outstanding Common Shares (Details) - Common stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended				12 Months Ended
	Nov. 30, 2018	May 31, 2018	May 31, 2017	Feb. 29, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock Dividends
Dividends declared per common share (in dollars per share)					$ 2.18	$ 2.10	$ 1.87
Reconciliation of Outstanding Common Shares
Outstanding shares at beginning of period					279.5	289.0	287.7
Shares issued					2.6	2.6	4.9
Treasury stock acquired					(5.5)	(12.1)	(3.6)
Outstanding shares at end of period					276.6	279.5	289.0
Common stock share repurchase disclosures
Share repurchase program, maximum authorized amount (in dollars)	$ 500.0	$ 300.0	$ 250.0	$ 400.0