EBPs Front Section and Obligation Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan
Percentage of eligible compensation the employer will match of employee contributions	6.00%
Employer's contributions charged to expense under defined contribution plan	$ 42	$ 36	$ 35
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax, noncash settlement charge	9	1	23
Change in benefit obligation:
Benefit obligation at beginning of year	1,237	1,187
Service cost	31	45	50
Interest cost	36	50	46
Plan participants’ contributions	0	0
Benefits paid	(41)	(111)
Net actuarial loss (gain)	47	69
Settlements	(127)	(3)
Net increase (decrease) in benefit obligation	(54)	50
Benefit obligation at end of year	1,183	1,237	1,187
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax, noncash settlement charge	0	0	0
Change in benefit obligation:
Benefit obligation at beginning of year	215	186
Service cost	1	1	1
Interest cost	7	8	7
Plan participants’ contributions	2	2
Benefits paid	(14)	(12)
Net actuarial loss (gain)	9	30
Settlements	0	0
Net increase (decrease) in benefit obligation	5	29
Benefit obligation at end of year	$ 220	$ 215	$ 186