Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Aggregate value	$ 5	$ 9	$ 12
Cash received for exercise price	$ 18	$ 59	$ 56
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance	1,889,045
Options exercised	(475,827)
Options expired	(147,808)
Ending Balance	1,265,410	1,889,045
Exercisable at December 31, 2020	1,265,410
Weighted Average Exercise Price (in usd per share)	$ 40.57	$ 40.43
Options Exercised, Weighted Average Exercise Price (in usd per share)	38.30
Options Expired, Weighted Average Exercise Price (in usd per share)	46.07
Shares Exercisable, Weighted Average Exercise Price (in usd per share)	$ 40.57
Shares Outstanding, Weighted Average Remaining Contractual Life	10 months 28 days	1 year 6 months 21 days
Shares Exercisable, Weighted Average Remaining Contractual Life	10 months 28 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 3	$ 10
Aggregate value	5
Shares Exercisable, Aggregate Intrinsic Value	$ 3