Employee Benefit Plans (Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	$ 10,230	$ 8,948
Purchases, sales, issuances and settlements, net	(55)	(5)
Estimated fair value of plan assets at December 31,	11,256	10,230
Pension Benefits \| Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	3,750
Estimated fair value of plan assets at December 31,	4,704	3,750
Pension Benefits \| Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	996
Estimated fair value of plan assets at December 31,	990	996
Pension Benefits \| Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	948
Estimated fair value of plan assets at December 31,	1,156	948
Pension Benefits \| Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1,177
Estimated fair value of plan assets at December 31,	1,101	1,177
Other Postretirement Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1,468	1,360
Purchases, sales, issuances and settlements, net	0	(3)
Estimated fair value of plan assets at December 31,	1,492	1,468
Other Postretirement Benefits \| Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	278
Estimated fair value of plan assets at December 31,	244	278
Other Postretirement Benefits \| Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	63
Estimated fair value of plan assets at December 31,	69	63
Other Postretirement Benefits \| Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	373
Estimated fair value of plan assets at December 31,	88	373
Other Postretirement Benefits \| Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	59
Estimated fair value of plan assets at December 31,	56	59
Level 3 \| Pension Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	686
Estimated fair value of plan assets at December 31,	708	686
Level 3 \| Pension Benefits \| Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	1
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	0	(1)
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Pension Benefits \| Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Pension Benefits \| Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	1
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	(3)	2
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Pension Benefits \| Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	0
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	0	0
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Pension Benefits \| Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	686	688
Realized gains (losses)	0	0
Unrealized gains (losses)	(55)	(1)
Purchases, sales, issuances and settlements, net	77	(1)
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	708	686
Level 3 \| Pension Benefits \| Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	1
Realized gains (losses)	0	0
Unrealized gains (losses)	0	(1)
Purchases, sales, issuances and settlements, net	0	0
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Other Postretirement Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	3
Estimated fair value of plan assets at December 31,	0	3
Level 3 \| Other Postretirement Benefits \| Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Other Postretirement Benefits \| Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 \| Other Postretirement Benefits \| Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	3
Estimated fair value of plan assets at December 31,	0	3
Level 3 \| Other Postretirement Benefits \| Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	$ 0	$ 0

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

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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 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.

+ References

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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

+ Details

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs.

+ References

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