Stock Incentive Plans - Schedule of Options (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Additional Disclosures
Total intrinsic value of options exercised	$ 3	$ 30	$ 38	$ 104
Stock Options
Number of Option Shares
Outstanding beginning of period (in shares)			2,933,501
Granted (in shares)			0
Issued due to Separation modification (in shares)			400,170
Exercised (in shares)			(768,302)
Canceled/Forfeited (in shares)			(14,607)
Expired (in shares)			(10,335)
Outstanding end of period (in shares)	2,540,427		2,540,427		2,933,501
Weighted Average Exercise Price
Weighted average exercise price - beginning of period (in dollars per share)			$ 32.54
Weighted average exercise price - granted (in dollars per share)			0.00
Weighted average exercise price - Issued due to Separation modification (in dollars per share)			31.72
Weighted average exercise price - exercised (in dollars per share)			37.33
Weighted average exercise price - cancelled/forfeited (in dollars per share)			48.33
Weighted average exercise price - expired (in dollars per share)			30.62
Weighted average exercise price - end of period (in dollars per share)	$ 30.88		$ 30.88		$ 32.54
Additional Disclosures
Weighted average remaining contractual life (in years)			4 years 10 months 2 days		5 years 2 months 27 days
Aggregate intrinsic value	$ 57		$ 57		$ 185
Total intrinsic value of options exercised			$ 38
Vested and Expected to Vest
Vested and expected to vest in the future as of period end (in shares)	2,539,930		2,539,930
Exercisable as of period end (in shares)	2,535,068		2,535,068
Weighted average exercise price vested and expected to vest as of period end (in dollars per share)	$ 30.88		$ 30.88
Weighted average exercise price exercisable as of period end (in dollars per share)	$ 30.83		$ 30.83
Weighted average remaining contractual life vested and expected to vest in the future as of period end (in years)			4 years 10 months 2 days
Weighted average remaining contractual life exercisable as of period end (in years)			4 years 10 months 2 days
Aggregate intrinsic value vested and expected to vest in the future as of period end	$ 57		$ 57
Aggregate intrinsic value exercisable as of period end	$ 57		$ 57