Employee Pension and Other Postretirement Benefits - Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Change in fair value of plan assets
Fair value of plan assets, beginning of year	$ 3,529	$ 3,854
Actual return on plan assets	754	(196)
Employer contributions	0	0
Plan participants' contributions	0	0
Benefits paid	(143)	(129)
Fair value of plan assets, end of year	$ 4,140	3,529
Pension Benefits \| Equity securities
Pension Plan and Other Postretirement Benefits Plan
Target plan asset allocation	53.00%
Pension Benefits \| Debt Securities
Pension Plan and Other Postretirement Benefits Plan
Target plan asset allocation	35.00%
Pension Benefits \| Real estate
Pension Plan and Other Postretirement Benefits Plan
Target plan asset allocation	12.00%
Other Benefits
Change in fair value of plan assets
Fair value of plan assets, beginning of year	$ 255	288
Actual return on plan assets	52	(18)
Employer contributions	0	0
Plan participants' contributions	4	4
Benefits paid	(20)	(19)
Fair value of plan assets, end of year	$ 291	$ 255
Other Benefits \| Equity securities
Pension Plan and Other Postretirement Benefits Plan
Target plan asset allocation	70.00%
Other Benefits \| Debt Securities
Pension Plan and Other Postretirement Benefits Plan
Target plan asset allocation	30.00%

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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- Definition

Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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- Definition

Amount of contributions received by defined benefit plan from participant which increases plan assets.

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- Definition

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.

+ References

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