Goodwill, Customer Relationships and Other Intangible Assets (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 9,354	$ 9,354
Gross carrying amounts of goodwill, customer relationships and other intangible assets	17,049
Amortization expense for intangible assets	$ 871	957	$ 1,029
Number of reporting units | segment	1
Weighted average cost of capital to calculate discount rate as of the measurement date (as a percent)	6.00%
Weighted average cost of capital, cost of equity (as a percent)	7.60%
Weighted average cost of capital, after-tax cost of debt (as a percent)	3.30%
Estimated amortization expense for intangible assets
2016	$ 725
2017	661
2018	587
2019	507
2020	435
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	2,435	3,039
Accumulated amortization	3,264	2,660
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	613	808
Accumulated amortization	$ 1,383	$ 1,247