Retirement Plans (Changes in Level 3 Retirement Plan Assets) (Details) - Significant Unobservable Inputs (Level 3) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	$ 282	$ 216
Unrealized gains, net	33	17
Realized losses, net	(1)
Purchases, sales and settlements, net	4	49
Fair value of assets at end of year	318	282
Private equity investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	26	20
Unrealized gains, net	5	5
Realized losses, net	0
Purchases, sales and settlements, net	2	1
Fair value of assets at end of year	33	26
Real Estate Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	84	68
Unrealized gains, net	7	6
Realized losses, net	(1)
Purchases, sales and settlements, net	0	10
Fair value of assets at end of year	90	84
Insurance Deposits Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	137	128
Unrealized gains, net	18	6
Realized losses, net	0
Purchases, sales and settlements, net	2	3
Fair value of assets at end of year	157	137
Retirement annuity contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	35	0
Unrealized gains, net	3	0
Realized losses, net	0
Purchases, sales and settlements, net	0	35
Fair value of assets at end of year	$ 38	$ 35

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

+ Details

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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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

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