Benefit Plans - Changes not yet recognized (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Pension benefits
Change in items not yet recognized as a component of defined benefit plans, net periodic cost
Prior service credit amortized to net cost	$ 56
Items not yet recognized as a component of net cost – December 31, 2018	(198)
Postretirement benefits
Change in items not yet recognized as a component of defined benefit plans, net periodic cost
Prior service credit amortized to net cost	21
Items not yet recognized as a component of net cost – December 31, 2018	$ (16)

Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration