Benefit Plans - Future amortization amounts (Details) $ in Millions	Dec. 31, 2020 USD ($)
Pension benefits
Estimates of the net actuarial loss (gain) and prior service credit expected to be recognized as a component of net periodic benefit cost during 2015
Prior service credit	$ 50
Postretirement benefits
Estimates of the net actuarial loss (gain) and prior service credit expected to be recognized as a component of net periodic benefit cost during 2015
Prior service credit	$ 25

Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (s)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant