Employee Benefit Plans (Estimated Cash Flows) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Estimated future benefit payments during 2019	$ 293
Estimated future benefit payments during 2020	308
Estimated future benefit payments during 2021	322
Estimated future benefit payments during 2022	322
Estimated future benefit payments during 2023	314
Estimated future benefit payments during 2024-2028	1,555
Nonqualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Estimated 2019 employer contributions	26
Estimated future benefit payments during 2019	26
Estimated future benefit payments during 2020	26
Estimated future benefit payments during 2021	25
Estimated future benefit payments during 2022	22
Estimated future benefit payments during 2023	21
Estimated future benefit payments during 2024-2028	94
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated 2019 employer contributions	28
Estimated future benefit payments during 2019	28
Estimated future benefit payments during 2020	27
Estimated future benefit payments during 2021	27
Estimated future benefit payments during 2022	26
Estimated future benefit payments during 2023	25
Estimated future benefit payments during 2024-2028	$ 117