Fair Value Measurements Fair Value Measurement (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Assets [Abstract]
Investments		$ 9,987	$ 15,351
Derivative contracts, at fair value (asset)	[1]	20	259
Assets, Fair Value Disclosure		9,705	15,287
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value		1,210	794
Other liabilities		112	3
Derivative contracts at fair value (liability)	[2]	768	36
Financial and Nonfinancial Liabilities, Fair Value Disclosure		2,090	833
Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Assets, Fair Value Disclosure		9,037	14,447
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value		1,154	794
Financial and Nonfinancial Liabilities, Fair Value Disclosure		1,154	794
Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Assets, Fair Value Disclosure		425	548
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value		56	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure		936	39
Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Assets, Fair Value Disclosure		243	292
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value		0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure		0	0
Other Segments and Holding Company [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative contracts, at fair value (asset)	[1]	0	0
Liabilities [Abstract]
Other liabilities		0	0
Derivative contracts at fair value (liability)	[2]	0	0
Other Segments and Holding Company [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative contracts, at fair value (asset)	[1]	20	259
Liabilities [Abstract]
Other liabilities		112	3
Derivative contracts at fair value (liability)	[2]	768	36
Other Segments and Holding Company [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative contracts, at fair value (asset)	[1]	0	0
Liabilities [Abstract]
Other liabilities		0	0
Derivative contracts at fair value (liability)	[2]	0	0
Other investments
Assets [Abstract]
Investments		9,685	15,028
Other investments | Other Segments and Holding Company [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Investments		9,037	14,447
Other investments | Other Segments and Holding Company [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Investments		405	289
Other investments | Other Segments and Holding Company [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Investments		$ 243	$ 292

[1] Amounts are classified within other assets in our condensed consolidated balance sheets.

[2] Amounts are classified within accrued expenses and other liabilities in our condensed consolidated balance sheets.