Employee Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure
Defined benefit plan, other information	8.85%
Assumed Health care plan pre age	65 years
Assumed Health care plan post age	65 years
Defined benefit plan, Actuarial gain (loss)	$ 1,100,000,000	$ (3,300,000,000)
Pension and other postretirement benefit plans, amounts that will be amortized from accumulated other comprehensive income (loss) in next fiscal year	$ 231,000,000
Defined benefit plan, description of direction and pattern of change for assumed health care cost trend rate	0.05
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	1.00%
Weighted average expected long-term rate of return on plan assets	9.00%
Profit sharing threshold	$ 2,500,000,000.0
Profit sharing	1,490,000,000	1,085,000,000	$ 506,000,000
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Defined benefit plan, estimated future employer contributions in next fiscal year	1,000,000,000
Contributions above minimum	500,000,000
Defined benefit plan, Actuarial gain (loss)	$ 88,000,000	$ (338,000,000)
Minimum | Growth-seeking assets
Defined Benefit Plan Disclosure
Defined benefit plan, target plan asset allocations	40.00%
Minimum | Income-generating assets
Defined Benefit Plan Disclosure
Defined benefit plan, target plan asset allocations	20.00%
Minimum | Risk-diversifying assets
Defined Benefit Plan Disclosure
Defined benefit plan, target plan asset allocations	25.00%
Maximum | Growth-seeking assets
Defined Benefit Plan Disclosure
Defined benefit plan, target plan asset allocations	50.00%
Maximum | Income-generating assets
Defined Benefit Plan Disclosure
Defined benefit plan, target plan asset allocations	30.00%
Maximum | Risk-diversifying assets
Defined Benefit Plan Disclosure
Defined benefit plan, target plan asset allocations	30.00%