Equity - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Aug. 31, 2016
Class of Stock [Line Items]
Non-cash expense recognized			$ 34,000,000	$ 30,000,000	$ 102,000,000	$ 90,000,000
Vested stock options (in shares)					3,186,709
Fair value of restricted stock					$ 199,000,000	$ 120,000,000
Authorized amount			1,200,000,000.0		1,200,000,000.0			$ 1,000,000,000.0
Remaining authorized repurchase amount			$ 241,000,000		$ 241,000,000
Repurchases of common stock (in shares)					11,469,042
Repurchases of common stock					$ 709,000,000		$ 50,000,000
Dividend per share (in dollars per share)			$ 0.20	$ 0.17	$ 0.60	$ 0.51
Payments of ordinary dividends, common stock					$ 358,000,000	$ 307,000,000
Employee Stock Option
Class of Stock [Line Items]
Intrinsic value of shares			$ 8,000,000	$ 5,000,000	15,000,000	$ 15,000,000
Unrecognized compensation expense			10,000,000		$ 10,000,000
Cost not yet recognized, period for recognition					1 year 9 months 6 days
Performance Based Restricted Stock Units
Class of Stock [Line Items]
Unrecognized compensation expense	$ 42,000,000		24,000,000		$ 24,000,000
Cost not yet recognized, period for recognition	3 years
Shares reserved for future issuance (in shares)	1,534,218
Vested stock options (in shares)	767,109
Stock-based compensation			6,000,000		18,000,000
Time Based And Performance Based Restricted Stock
Class of Stock [Line Items]
Unrecognized compensation expense			$ 171,000,000		$ 171,000,000
Cost not yet recognized, period for recognition					1 year 7 months 6 days
Maximum | Performance Based Restricted Stock Units
Class of Stock [Line Items]
Unrecognized compensation expense	$ 85,000,000
Scenario, Forecast | Performance Based Restricted Stock Units
Class of Stock [Line Items]
Amount remaining in fiscal period		$ 6,000,000