Share-Based Compensation - Compensation Expense Table (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	$ 150		$ 235		$ 172
Income tax benefit	35		86		64
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	145	[1]	175	[1]	157
Restricted Stock [Member] | Share Based Compensation [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense			31
Stock Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	17	[1]	20	[1]	19
Stock Option [Member] | Share Based Compensation [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense			1
Other Equity-Classified Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	1		2		1
Value Creation Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	0		0		(4)
Performance-Based Unit Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	(13)	[1]	38	[1]	$ (1)
Performance-Based Unit Awards [Member] | Share Based Compensation [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	$ (7)		$ 7

[1] Includes restructuring charges of $(7) million for performance-based unit awards in 2017 and $31 million for restricted stock, $1 million for stock options, and $7 million for performance-based unit awards in 2016. See Note 18—Restructuring Charges for further discussion.