Retirement Plans (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Benefit liability other supplement retirement plans	$ 5	$ 5
Shares of company common stock | shares	0	233,849
Rate of employee contribution from earnings	80.00%
Matching contribution allocation rate first time	100.00%
Employee contribution rate for first time matching	3.00%
Matching contribution allocation rate second time	50.00%
Employees contribution rate for second time matching	3.00%
Employer contribution in common stock	$ 33	$ 29	$ 26
Minimum range of eligible compensation for noncontributory profit sharing feature	0.00%
Maximum range of eligible compensation for noncontributory profit sharing feature	3.50%
Accrued profit sharing expense	$ 16	$ 17	$ 11
Contribution rate of profit sharing expenses	0.0225	0.0250	0.0175
Limited Liability Partnerships [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount		$ 4
Common Stock [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	$ 0	10
Common Stock [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount		15
Debt Investments [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	$ 166	$ 116