Post-retirement and Similar Obligations - Schedule of Aggregate PBO and ABO and Fair Value of Plan Assets for Underfunded Plans (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Projected benefit obligation	$ 3,819	$ 3,669
Fair value of plan assets	3,092	2,848
Accumulated benefit obligation	3,629	3,451
Fair value of plan assets	$ 3,092	$ 2,848

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Amount of plan asset for defined benefit pension plan with projected benefit obligation in excess of plan assets.

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Amount of projected benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets.

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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-Publisher FASB
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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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