Employee Benefit Plans (Paid Benefit Obligations and Accumulated Benefit Obligations in Excess of Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accumulated benefit obligation [Abstract]
Projected benefit obligations	$ 2,227	$ 1,999
Accumulated benefit obligations	2,113	1,906
Estimated fair value of plan assets	430	280
Defined Benefit Plan, Plan with Accumulated Postretirement Benefit Obligation in Excess of Plan Assets, Accumulated Postretirement Benefit Obligation	812	724
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligations	2,287	2,021
Accumulated benefit obligations	2,162	1,921
Estimated fair value of plan assets	487	301
Defined Benefit Plan, Plan with Accumulated Postretirement Benefit Obligation in Excess of Plan Assets, Plan Assets	$ 375	$ 388