Supplemental Quarterly Financial Data - Supplemental Quarterly Financial Data (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Quarterly Financial Data [Line Items]
Revenues and other	$ 4,391	$ 4,179	$ 3,972	$ 4,536	$ 4,297	$ 4,328	$ 4,338	$ 3,925	$ 17,078	$ 16,888	$ 12,092
Expenses	3,723	3,999	3,616	3,739	3,108	3,326	3,079	2,791	15,077	12,304
NET INCOME	668	180	356	797	1,189	1,002	1,259	1,134	2,001	4,584	3,032
Income attributable to common stock	$ 649	$ 161	$ 337	$ 778	$ 1,170	$ 983	$ 1,240	$ 1,115	$ 1,925	$ 4,508	$ 3,000
NET INCOME PER COMMON SHARE:
Basic	$ 1.66	$ 0.41	$ 0.87	$ 2.02	$ 3.05	$ 2.56	$ 3.23	$ 2.91	$ 4.95	$ 11.75	$ 8.53
Diluted	$ 1.64	$ 0.41	$ 0.86	$ 2.00	$ 2.98	$ 2.50	$ 3.17	$ 2.86	$ 4.92	$ 11.47	$ 8.46