Employee Stock-Based Incentives - Cash Flows and Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit from compensation expense	$ 746	$ 854	$ 865
Employee Stock Option
Cash received from the exercise of stock options under all stock-based incentive arrangements, and the actual income tax benefit realized related to tax deductions from the exercise of the stock options
Cash received for options exercised	20	63	166
Tax benefit realized	$ 64	$ 104	$ 42