Pensions Benefit Plans and Other Postretirement Benefits - Changes in Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
U.S. Pension Plans
Changes in fair value of pension plan assets
Fair value at beginning of year	$ 1,654	$ 1,909
Actual gain (loss) on plan assets	254	118
Benefit payments	(128)	(175)
Employer contributions	7	2
Settlements	(393)	(200)
Net change in fair value of assets	(260)	(255)
Fair value at end of year	1,394	1,654
Non-U.S. Pension Plans
Changes in fair value of pension plan assets
Fair value at beginning of year	1,011	1,012
Actual gain (loss) on plan assets	87	139
Benefit payments	(60)	(71)
Employer contributions	24	38
Participant contributions	1	2
Settlements	(171)
Foreign currency translation	83	(111)
Other		2
Net change in fair value of assets	(36)	(1)
Fair value at end of year	$ 975	$ 1,011