Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions					1 Months Ended			2 Months Ended	3 Months Ended			9 Months Ended	12 Months Ended
	May 19, 2017	May 10, 2017	Nov. 20, 2016	Jan. 15, 2016	Mar. 31, 2017	Nov. 30, 2016	Mar. 31, 2016	Jan. 15, 2016	May 19, 2017	Mar. 31, 2017	Dec. 30, 2016	Nov. 30, 2016	Mar. 31, 2017	Apr. 01, 2016	Apr. 03, 2015	Nov. 30, 2015
Class of Stock [Line Items]
Dollar amount of shares repurchased													$ 0	$ 368,000,000	$ 500,000,000
Special dividend, declared and paid (in usd per share)										$ 4.00
Cash dividends declared per common share (in usd per share)													$ 0.3	$ 4.6	$ 0.6
Authorization to repurchase common stock			$ 1,300,000,000.0
Stock Repurchase Program, Authorized Amount, Remainder of Fiscal Year			500,000,000
Payments for repurchases of common stock													$ 500,000,000	$ 1,868,000,000	$ 500,000,000
Repurchases of common stock (in shares)													0.0	17.0	21.0
Average price paid per share (in usd per share)													$ 0.00	$ 21.69	$ 23.73
Remaining authorization at end of period					$ 800,000,000					$ 800,000,000			$ 800,000,000	$ 790,000,000	$ 1,158,000,000
Common Stock | Subsequent Event
Class of Stock [Line Items]
Cash dividends declared per common share (in usd per share)		$ 0.075
2016 Stock Repurchase Program
Class of Stock [Line Items]
Accelerated Share Repurchase Program, Adjustment			$ 510,000,000
March 2017 Accelerated Stock Repurchase Agreement [Member]
Class of Stock [Line Items]
Dollar amount of shares repurchased					500,000,000
Authorization to repurchase common stock					$ 500,000,000					500,000,000			500,000,000
Repurchases of common stock (in shares)					14.2
Remaining authorization at end of period					$ 800,000,000					800,000,000			$ 800,000,000
March 2017 Accelerated Stock Repurchase Agreement [Member] | Subsequent Event
Class of Stock [Line Items]
Repurchases of common stock (in shares)	2.2								16.4
Average price paid per share (in usd per share)									$ 30.51
November 2015 Accelerated Stock Repurchase Agreement
Class of Stock [Line Items]
Authorization to repurchase common stock																$ 500,000,000
Payments for repurchases of common stock											$ 500,000,000
Repurchases of common stock (in shares)				5.0				24.9			19.9
Average price paid per share (in usd per share)								$ 20.08
March 2016 Accelerated Stock Repurchase Agreement
Class of Stock [Line Items]
Authorization to repurchase common stock							$ 1,000,000,000.0
Payments for repurchases of common stock										$ 1,000,000,000
Repurchases of common stock (in shares)						6.5	42.4					48.9
Average price paid per share (in usd per share)												$ 20.44