Employee Benefit Plans (Accumulated Other Comprehensive Loss Pretax Amounts Not Yet Reflected in Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial losses	$ 920	$ 800
Accumulated prior service cost (credit)	2	2
Total	922	802
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial losses	166	113
Accumulated prior service cost (credit)	(138)	(178)
Total	$ 28	$ (65)