Retirement Plans (Changes in Level 3 Retirement Plan Assets) (Details) - Significant Unobservable Inputs (Level 3) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	$ 216	$ 189
Unrealized gains (losses), net	17	(1)
Realized gains, net		3
Purchases, sales, and settlements, net	49	25
Fair value of assets at end of year	282	216
Private equity investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	20	18
Unrealized gains (losses), net	5	0
Realized gains, net		0
Purchases, sales, and settlements, net	1	2
Fair value of assets at end of year	26	20
Real Estate Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	68	51
Unrealized gains (losses), net	6	(1)
Realized gains, net		0
Purchases, sales, and settlements, net	10	18
Fair value of assets at end of year	84	68
Insurance Deposits Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	128	120
Unrealized gains (losses), net	6	0
Realized gains, net		3
Purchases, sales, and settlements, net	3	5
Fair value of assets at end of year	137	128
Retirement annuity contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of year	0	0
Unrealized gains (losses), net	0	0
Realized gains, net		0
Purchases, sales, and settlements, net	35	0
Fair value of assets at end of year	$ 35	$ 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

+ 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
-Publisher FASB
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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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