Retirement Benefits Pension Plan Contributions (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Unfunded Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 350
Pension Plan | Funded Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	175
Pension Plan | Unfunded Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	86
Minimum | Pension Plan | Funded Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	500
Maximum | Pension Plan | Funded Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 700