Employee Benefit Plans - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Apr. 24, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		14			17
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options		$ 131	$ 75
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years
Performance Stock Units, Grants in Period		1	1	2
Performance Stock Unit, Unrecognized Compensation Expense		$ 10
Deferred losses related to NCF Retirement Plan settlement	[1]	$ 60	$ 0	$ 0
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year		7.25%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate		7 years
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate		4.50%
Defined Benefit Plan, Effect of 25 Basis Point Change in Expected Long-Term Return on Plan Assets		$ 8
Defined Benefit Plan, Effect of 25 Basis Point Change in the Discount Rate		$ 1
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		6.00%	6.00%	6.00%
Defined Contribution Plan, Cost		$ 112	$ 130	$ 105
Pension Plan [Member]
Deferred losses related to NCF Retirement Plan settlement		$ (60)	$ 0	$ 0
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate		5.25%	5.90%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		5.90%	6.66%	6.68%
Other Postretirement Benefits Plan [Member]
Deferred losses related to NCF Retirement Plan settlement		$ 0	$ 0	$ 0
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate		3.27%	3.10%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		3.10%	3.12%	3.13%
Long-term [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense		$ 235	$ 319	$ 291
Short-term [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense		$ 466	$ 476	$ 469

[1] Related to the Company's NCF Retirement Plan settlement in the fourth quarter of 2018. See Note 17, "Employee Benefit Plans," for additional information.