Amount of contribution received by defined benefit plan from employer which increases plan assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Amount of cost for defined contribution plan.

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Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan expenses	$ 79	$ 77	$ 77
Pension
Defined Benefit Plan Disclosure [Line Items]
Company contributions	178	70
Expected company contributions	26
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Company contributions	6	$ 4
Expected company contributions	$ 5
Minimum \| Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	15.00%
Minimum \| Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	75.00%
Minimum \| Other plan assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	0.00%
Maximum \| Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	25.00%
Maximum \| Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	85.00%
Maximum \| Other plan assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	10.00%
United States \| Pension
Defined Benefit Plan Disclosure [Line Items]
Company contributions	$ 115