Goodwill, Customer Relationships and Other Intangible Assets (Details) $ in Millions		12 Months Ended
	Oct. 31, 2016	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Finite-Lived Intangible Assets [Line Items]
Goodwill		$ 9,354	$ 9,354
Gross carrying amounts of goodwill, customer relationships and other intangible assets		17,034
Amortization expense for intangible assets		$ 767	871	$ 957
Number of reporting units	1	1
Weighted average cost of capital - discount rate (as a percent)	6.00%
After-tax cost of debt component of discount rate (as a percent)	2.80%
Cost of equity component of discount rate (as a percent)	6.20%
Estimated amortization expense for intangible assets
2017		$ 652
2018		584
2019		509
2020		440
2021		127
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		1,877	2,435
Accumulated amortization		3,822	3,264
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		471	613
Accumulated amortization		$ 1,510	$ 1,383