Schedule Summarizing Quarterly Operation Results (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 12,328	$ 12,238	$ 12,222	$ 11,712	$ 10,187	$ 10,319	$ 10,321	$ 10,486	$ 48,500	$ 41,313	$ 39,126
Income before income taxes	287	551	646	686	(49)	586	654	730	2,170	1,921	1,911
Net income	$ 145	$ 290	$ 344	$ 368	$ (30)	$ 368	$ 420	$ 473	$ 1,147	$ 1,231	$ 1,222
Basic earnings (loss) per common share (in dollars per share)	$ 0.96	$ 1.87	$ 2.22	$ 2.37	$ (0.19)	$ 2.34	$ 2.66	$ 2.97	$ 7.44	$ 7.81	$ 7.56
Diluted earnings (loss) per common share (in dollars per share)	$ 0.94	$ 1.85	$ 2.19	$ 2.35	$ (0.19)	$ 2.31	$ 2.63	$ 2.95	$ 7.36	$ 7.73	$ 7.47