Employee Benefit Plans (Estimated Cash Flows) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Estimated future benefit payments during 2018	$ 295
Estimated future benefit payments during 2019	303
Estimated future benefit payments during 2020	315
Estimated future benefit payments during 2021	318
Estimated future benefit payments during 2022	318
Estimated future benefit payments during 2023-2027	1,573
Nonqualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Estimated 2018 employer contributions	28
Estimated future benefit payments during 2018	28
Estimated future benefit payments during 2019	25
Estimated future benefit payments during 2020	24
Estimated future benefit payments during 2021	23
Estimated future benefit payments during 2022	22
Estimated future benefit payments during 2023-2027	100
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated 2018 employer contributions	26
Estimated future benefit payments during 2018	26
Estimated future benefit payments during 2019	27
Estimated future benefit payments during 2020	27
Estimated future benefit payments during 2021	26
Estimated future benefit payments during 2022	26
Estimated future benefit payments during 2023-2027	123
Reduction in PNC Benefit Payments Due to Medicare Part D Subsidy, 2023 - 2027	$ 2