Employee Benefits (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit expense	$ 8	$ 11	$ 15
Contributions by employer	$ 167	170	$ 146
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Number of eligible employees for pension plan (in employee) | employee	0
Defined benefit obligation	$ 1,370	1,210
Defined benefit overfunded (underfunded) status	10	(1)
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit obligation	88	12
Defined benefit overfunded (underfunded) status	(88)	(12)
SERP
Defined Benefit Plan Disclosure [Line Items]
Defined benefit obligation	10	110
Defined benefit overfunded (underfunded) status	$ (10)	$ (110)