Share-Based Compensation - Compensation Expense Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	$ 325	$ 155	$ 320
Income tax benefit	120	57	117
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	144	122	103
Stock Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	21	27	43
Other Equity-Classified Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	1	1	1
Value Creation Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	136	0	(2)
Performance-Based Unit Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	23	4	8
Other Performance-Based Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	0	0	165
Other Liability-Classified Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Pretax compensation expense	$ 0	$ 1	$ 2