Share-Based Compensation (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Number of Stock Options
Outstanding at Beginning of period (in shares)			379,102
Exercised (in shares)	(25,113)	(9,216)	(80,378)	(62,624)
Forfeited (in shares)			(435)
Outstanding at End of period (in shares)	298,289		298,289		379,102
Exercisable (in shares)	298,289	300,000	298,289	300,000
Weighted-Average Exercise Price
Weighted average exercise price, outstanding, beginning of period (in dollars per share)			$ 54.32
Exercised (in dollars per share)			23.82
Forfeited (in dollars per share)			19.75
Weighted average exercise price, outstanding, end of period (in dollars per share)	$ 62.59		62.59		$ 54.32
Options exercisable, weighted average exercise price (in dollars per share)	$ 62.59	$ 49.76	$ 62.59	$ 49.76
Weighted-Average Remaining Contractual Term (In Years) [Abstract]
Weighted-Average Remaining Contractual Term, Outstanding (in years)			5 years 8 months 8 days		5 years 3 months 7 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)			5 years 8 months 8 days
Aggregate Intrinsic Value (In Millions) [Abstract]
Aggregate Intrinsic Value, Outstanding (in millions)	$ 18		$ 18		$ 20
Exercisable, aggregate intrinsic value	$ 18		$ 18