Pension and Postretirement Benefit Plans - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2017 item	Mar. 31, 2017 USD ($)	Mar. 31, 2014 item	Dec. 31, 2016	Mar. 31, 2011 LimitedPartnership
Maximum
Benefit Plan Information
Estimated pension and postretirement employer contributions in current fiscal year		$ 500
Minimum
Benefit Plan Information
Estimated pension and postretirement employer contributions in current fiscal year		300
WG Trading Company
Benefit Plan Information
Number of insurers 3M and certain benefit plans filed lawsuits on seeking insurance coverage for the WG Trading Company claim | item			5
Number of additional limited partners of WG Trading Company, in addition to 3M, who objected and appealed the court's order to the United States Court of Appeals for the Second Circuit | LimitedPartnership					6
WG Trading Company | Maximum
Benefit Plan Information
Percentage of WG Trading Company holdings in relation to total fair value of the company's total plan assets, high end of range (as a percent)				0.50%
Panda Temple Power LLC
Benefit Plan Information
Number of entities in which the U.S. pension and postretirement benefit plans have invested in that filed for chapter 11 bankruptcy protection | item	1
Panda Temple Power LLC | Maximum
Benefit Plan Information
Percentage of investment in relation to the fair value of the U.S. pension and postretirement benefit plans' assets at the most recent measurement date				1.00%
Qualified and Non-qualified Pension Benefits
Benefit Plan Information
Company contributions year to date		247
Postretirement Benefits
Benefit Plan Information
Company contributions year to date		$ 1