Employee Benefit Plans (Paid Benefit Obligations and Accumulated Benefit Obligations in Excess of Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accumulated benefit obligation [Abstract]
Projected benefit obligations	$ 2,441	$ 2,227
Accumulated benefit obligations	2,312	2,113
Estimated fair value of plan assets	539	430
Defined Benefit Plan, Plan with Accumulated Postretirement Benefit Obligation in Excess of Plan Assets, Accumulated Postretirement Benefit Obligation	868	812
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligations	2,469	2,287
Accumulated benefit obligations	2,332	2,162
Estimated fair value of plan assets	564	487
Defined Benefit Plan, Plan with Accumulated Postretirement Benefit Obligation in Excess of Plan Assets, Plan Assets	$ 355	$ 375