Stockholders' Equity - Capital Stock and Share Repurchases (Details) - USD ($)	3 Months Ended				6 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Nov. 08, 2018	Apr. 03, 2017
Equity [Abstract]
Initial authorization								$ 2,000,000,000.0
Additional authorization							$ 2,000,000,000.0
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)	6,220,190	7,359,609	1,448,729	3,779,194	13,579,799	5,227,923
Average price per share (in dollars per share)	$ 40.18	$ 54.35	$ 87.16	$ 85.86	$ 47.86	$ 86.22
Amount	$ 150,000,000	$ 400,000,000	$ 127,000,000	$ 324,000,000	$ 650,000,000	$ 451,000,000
Accrued liability for shares purchased but not yet settled in cash			$ 9,000,000			$ 9,000,000
Open market purchases
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)	4,414,840	5,510,415	1,448,729	3,779,194
Average price per share (in dollars per share)	$ 33.96	$ 54.44	$ 87.16	$ 85.86
Amount	$ 250,000,000	$ 300,000,000	$ 127,000,000	$ 324,000,000
ASR
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of shares		200,000,000
Prepayments for share repurchases		$ 100,000,000
Number of shares repurchased (in shares)	1,805,350	1,849,194	0	0	3,654,544
Average price per share (in dollars per share)	$ 55.39	$ 54.08	$ 0	$ 0	$ 54.73
Amount	$ 100,000,000	$ 100,000,000	$ 0	$ 0	$ 200,000,000