Employment Benefit Plans Assumptions Used (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - expense			3.79%	4.50%	3.75%
Expected Long-term Return on Assets - expense			6.60%	6.75%	6.75%
Rate of Compensation Increase - expense			3.80%	3.80%	3.80%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount Rate - benefit obligations			4.22%	3.79%
Rate of Compensation Increase - benefit obligations			3.80%	3.80%
Assumptions Sensitivity Analysis [Abstract]
Effect of 50 basis point decrease in discount rate			$ 1
Effect of 50 basis point increase in discount rate			(1)
Effect of 50 basis point decrease in rate of return on plan assets			11
Effect of 50 basis point increase in rate of return on plan assets			$ (11)
Retiree Health and Welfare Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - expense			3.69%	4.50%	3.75%
Rate of Compensation Increase - expense			3.80%	3.80%	3.80%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount Rate - benefit obligations			4.09%	3.69%
Rate of Compensation Increase - benefit obligations			3.80%	3.80%
Assumptions Sensitivity Analysis [Abstract]
Effect of 50 basis point decrease in discount rate			$ 1
Effect of 50 basis point increase in discount rate			$ (1)
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Assumed health care cost trend rate for next year (participants over 65)	[1]		3.00%	3.00%	3.00%
Assumed health care cost trend rate for next year (participants under 65)			7.70%	7.90%	8.20%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate			4.50%	4.50%	4.50%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate			2038	2028	2028
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components			$ 1
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components			(1)
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation			19
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation			$ (16)
Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - expense		4.22%
Expected Long-term Return on Assets - expense		6.63%
Scenario, Forecast [Member] | Retiree Health and Welfare Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - expense		4.09%

[1] Effective January 1, 2013, Medicare-eligible retirees who are enrolled in the retiree medical program received a contribution to a Health Reimbursement Account, which can be used to reimburse plan participants for health insurance premiums and to pay eligible out-of-pocket expenses.