Summary of Significant Accounting Policies (Components of Fixed Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,394	$ 2,448
Less-accumulated depreciation and amortization	(1,621)	(1,639)
Property, plant and equipment, net	773	809	$ 828
Furniture and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,133	1,193
Land and Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	396	401
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 865	$ 854
Minimum | Furniture and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Minimum | Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	30 years
Maximum | Furniture and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Maximum | Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years