Accumulated Other Comprehensive Income - Reclassifications out of other comprehensive income (loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive (Income) Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit Plans, Net Of Tax	$ 88	$ 189
Other Comprehensive (Income) Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit Plans, Tax	$ 23	$ 50

Amount, after tax, of reclassification adjustment from accumulated other comprehensive (income) loss for net periodic benefit cost (credit) of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Publisher FASB
-Name Accounting Standards Codification
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