Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
Summary of Significant Accounting Policies [Line Items]
Income tax benefit	[1]	$ (1,296)	$ (1,104)	$ (832)
Accounting Standards Update 2016-09 [Member]
Summary of Significant Accounting Policies [Line Items]
Income tax benefit		$ 87
Accounting Standards Update 2014-09 [Member] | Subsequent Event [Member]
Summary of Significant Accounting Policies [Line Items]
Capitalized costs					$ 219
Deferred tax liability					$ 51
Furniture and equipment [Member] | Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life, property, plant and equipment		5 years
Furniture and equipment [Member] | Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life, property, plant and equipment		10 years
Buildings [Member] | Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life, property, plant and equipment		20 years
Buildings [Member] | Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life, property, plant and equipment		40 years
Software [Member] | Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life, Software and certain costs incurred for purchasing or developing software		3 years
Software [Member] | Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life, Software and certain costs incurred for purchasing or developing software		5 years

[1] Includes the prospective adoption of ASU 2016-09 in 2017. See New Accounting Standards in Note 2 for additional information. Taxes on income were increased by approximately $46 million in December 2017 due to the enactment of the Tax Cuts and Jobs Act legislation resulting in the remeasurement of deferred tax assets and other tax adjustments.