Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Assets measured at fair value on a recurring basis

	December 31, 2018								December 31, 2017
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets	(in millions)
Investments (Note 4)	$	7,493	$	317	$	372	$	8,182	$	9,378	$	264	$	278	$	9,920
Derivative contracts, at fair value (Note 6)(1)	7		517		—		524		—		—		—		—
	$	7,500	$	834	$	372	$	8,706	$	9,378	$	264	$	278	$	9,920
Liabilities
Securities sold, not yet purchased (Note 4)	$	468	$	—	$	—	$	468	$	988	$	35	$	—	$	1,023
Other liabilities	—		2		—		2		—		1		—		1
Derivative contracts, at fair value (Note 6)	—		36		—		36		36		1,239		—		1,275
	$	468	$	38	$	—	$	506	$	1,024	$	1,275	$	—	$	2,299

⁽¹⁾  Amounts are classified within other assets in our consolidated balance sheets.

Assets measured at fair value on a recurring basis for which we use Level 3 inputs to determine fair value

	Year Ended December 31,
	2018			2017
	(in millions)
Balance at January 1	$	278		$	211
Net unrealized gains	95			67
Other	(1		)	—
Balance at December 31	$	372		$	278