Employee Benefits (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit expense	$ 25	$ 8	$ 11
Contributions by employer	$ 168	167	$ 170
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Number of eligible employees for pension plan (in employee) | employee	0
Defined benefit obligation	$ 1,530	1,370
Defined benefit overfunded (underfunded) status	15	(10)
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit obligation	69	10
Defined benefit overfunded (underfunded) status	(69)	(10)
SERP
Defined Benefit Plan Disclosure [Line Items]
Defined benefit obligation	4	88
Defined benefit overfunded (underfunded) status	$ (4)	$ (88)