Employee Stock-Based Incentives - Cash Flows and Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit from compensation expense	$ 854	$ 865	$ 1,000
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 from options exercised	63	166	333
Tax benefit realized	$ 104	$ 42	$ 53