Benefit Plans (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment	$ 277,000,000
One-time settlement charge relating to lump sum distributions					$ 81,000,000
Amounts charged to expense for defined contribution plans			$ 78,000,000	$ 85,000,000	83,000,000
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation			8,400,000,000	7,400,000,000
Projected benefit obligation			8,522,000,000
Accumulated benefit obligation			357,000,000	7,239,000,000
Fair value of plan assets			134,000,000	7,012,000,000
Defined benefit plan, plan assets, amount	8,015,000,000		$ 8,167,000,000	$ 7,138,000,000	$ 8,015,000,000
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets			7.80%	7.80%	8.00%
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets				$ 8,023,000,000
Pension [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions			$ 30,000,000
Pension [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Composition of plan assets			1.00%
Pension [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Composition of plan assets			5.00%
Pension [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation percentage			30.00%			55.00%
Pension [Member] | Equity Securities [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Composition of plan assets			1.00%
Pension [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation percentage			70.00%			45.00%
Pension [Member] | Fixed Income Securities [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Composition of plan assets			8.00%
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 270,000,000		$ 213,000,000	$ 211,000,000	$ 270,000,000
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets			7.80%	7.80%	0.00%
Postretirement Benefit Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions			$ 60,000,000
Postretirement Benefit Plan [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount			$ 0
Postretirement Benefit Plan [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Composition of plan assets			4.00%
Postretirement Benefit Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation percentage						55.00%
Postretirement Benefit Plan [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation percentage						45.00%
Postretirement Benefit Plan [Member] | Fixed Income Securities [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Composition of plan assets			8.00%
Level 3 [Member] | Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount			$ 0	$ 0
Forecast [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets		6.60%
Forecast [Member] | Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets		7.70%