Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Benefit Plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan, net	100.00%
Cost of defined benefit plans	$ 552	$ 532	$ 499
Defined benefit plan cost	8	11	9
Defined benefit plan obligation	$ 96	63
Defined Contribution Benefit Plans [Member] | Minimum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	3.00%
Defined Contribution Benefit Plans [Member] | Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	9.00%
Restoration Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Number of hours of service required to qualify for the plan	1,000 or more hours
Noncontributory and nonqualified plan, benefit expense	$ 35	44	22
Noncontributory and nonqualified plan, accrued benefits liabilities	242	227
Supplemental Executive Retirement Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan cost	24	19	$ 26
Defined benefit plan obligation	$ 204	$ 192