Employee Benefit Plans (Paid Benefit Obligations and Accumulated Benefit Obligations in Excess of Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accumulated benefit obligation [Abstract]
Projected benefit obligations	$ 1,999	$ 1,996
Accumulated benefit obligations	1,906	1,890
Estimated fair value of plan assets	280	266
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligations	2,021	2,016
Accumulated benefit obligations	1,921	1,904
Estimated fair value of plan assets	$ 301	$ 285