Employee Benefit Plans - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 22, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		16			17
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options		$ 75	$ 65
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years
Performance Stock Units, Grants in Period		1	2	1
Performance Stock Unit, Unrecognized Compensation Expense		$ 56
Personal Pension Account Interest Crediting Rate		3.11%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year		8.25%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate		8 years
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate		4.50%
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation		$ 1
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation		1
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components		1
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components		1
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		$ 130	$ 105	$ 121
Restricted Stock Unit Expense		83	56	46
Performance Stock Units Expense	[1]	77	67	32
Restricted Stock or Unit Expense		0	2	16
Stock or Unit Option Plan Expense		0	0	1
Share-based Compensation		160	125	95
Pension Plan [Member]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		$ 23
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate		5.90%
Defined Benefit Plan, Plan Assets, Contributions by Employer	[2]	$ 9	5
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year		$ 7
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate		3.10%
Defined Benefit Plan, Plan Assets, Contributions by Employer	[3]	$ 0	0
Long-term [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense		319	291	245
Short-term [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense		$ 476	$ 469	$ 448

[1] Phantom stock units are settled in cash. The Company paid $80 million, $28 million, and $16 million during the years ended December 31, 2017, 2016, and 2015, respectively, related to these share-based liabilities.

[2] Employer contributions represent the benefits that were paid to nonqualified plan participants. Unfunded nonqualified supplemental pension plans are not funded through plan assets.

[3] The Company contributed less than $1 million to the other postretirement benefits plans during both 2017 and 2016.