Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Contributions to defined contribution plans	$ 33	$ 34	$ 40
Expected benefit plan payments for each of the next five years	57
Benefit plan payments expected to be funded from cash and cash equivalents and other assets for next fiscal year	17
Expected total benefit plan payments for five years after the next five years	264
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 745	694	$ 685
Pension Benefits [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	85.00%
Pension Benefits [Member] | Fixed Income Securities [Member] | Level 1 Inputs [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 617	240
Pension Benefits [Member] | Fixed Income Securities [Member] | Level 2 Inputs [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		233
Pension Benefits [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	15.00%
Fair value of plan assets	$ 110	112
Pension Benefits [Member] | Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 18	$ 109
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan health care cost trend rate assumed for next fiscal year	6.90%
Defined benefit plan ultimate health care cost trend rate	5.00%