Shared-Based Compensation - Narrative (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Non-cash expense recognized			$ 35	$ 32	$ 64	$ 61
Fair value of restricted stock					160	195
Performance Based Restricted Stock Units
Class of Stock [Line Items]
Unrecognized compensation expense	$ 41	$ 41	32		32
Cost not yet recognized, period for recognition		3 years
Vested stock options (in shares)		600,000
Stock-based compensation			6		9
Amount of non-cash compensation remaining in fiscal period			13		$ 13
Time Based Restricted Units
Class of Stock [Line Items]
Vested stock options (in shares)					1,000,000
Time Based And Performance Based Restricted Stock
Class of Stock [Line Items]
Unrecognized compensation expense			167		$ 167
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	$ 82	$ 82
Shares reserved for future issuance (in shares)	1,100,000	1,100,000
Employee Stock Option
Class of Stock [Line Items]
Intrinsic value of shares			10	$ 10	$ 18	$ 19
Unrecognized compensation expense			$ 12		$ 12
Cost not yet recognized, period for recognition					1 year 10 months 24 days
Bakkt
Class of Stock [Line Items]
Unrecognized compensation expense	$ 45	$ 45
Cost not yet recognized, period for recognition	8 years
Preferred units, issued	101,000,000	101,000,000
Common units, issued	4,000,000	4,000,000
Phantom incentive units, issued	3,000,000	3,000,000