Postretirement Benefits (Details 9) - Employee pension plan	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Target asset allocation for the portfolio:
Total plan assets (as a percent)	100.00%	100.00%
Actual asset allocation for the portfolio:
Total plan assets (as a percent)	100.00%	100.00%
Total equity securities
Target asset allocation for the portfolio:
Total plan assets (as a percent)	55.00%	55.00%
Actual asset allocation for the portfolio:
Total plan assets (as a percent)	56.00%	56.00%
U.S. equity securities
Target asset allocation for the portfolio:
Total plan assets (as a percent)	35.00%	35.00%
Actual asset allocation for the portfolio:
Total plan assets (as a percent)	38.00%	36.00%
U.S. small capitalization core equity
Target asset allocation for the portfolio:
Total plan assets (as a percent)	22.00%
U.S. large capitalization core equity
Target asset allocation for the portfolio:
Total plan assets (as a percent)	30.00%
U.S. equity index
Target asset allocation for the portfolio:
Total plan assets (as a percent)	48.00%
Non-U.S. equity securities
Target asset allocation for the portfolio:
Total plan assets (as a percent)	20.00%	20.00%
Actual asset allocation for the portfolio:
Total plan assets (as a percent)	18.00%	20.00%
International small capitalization risk controlled equity
Target asset allocation for the portfolio:
Total plan assets (as a percent)	11.00%
International emerging markets equity
Target asset allocation for the portfolio:
Total plan assets (as a percent)	11.00%
International risk controlled equity
Target asset allocation for the portfolio:
Total plan assets (as a percent)	78.00%
Debt securities
Target asset allocation for the portfolio:
Total plan assets (as a percent)	44.00%	44.00%
Actual asset allocation for the portfolio:
Total plan assets (as a percent)	43.00%	43.00%
U.S. Treasury Strips
Target asset allocation for the portfolio:
Total plan assets (as a percent)	44.00%
U.S. corporate bonds with an emphasis on long duration bonds rated A or better
Target asset allocation for the portfolio:
Total plan assets (as a percent)	44.00%
Floating rate high income leverage loans
Target asset allocation for the portfolio:
Total plan assets (as a percent)	12.00%
Other
Target asset allocation for the portfolio:
Total plan assets (as a percent)	1.00%	1.00%
Actual asset allocation for the portfolio:
Total plan assets (as a percent)	1.00%	1.00%