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			36 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues and other	$ 3,576	$ 4,019	$ 4,383	$ 4,076	$ 4,391	$ 4,179	$ 3,972	$ 4,536	$ 16,054	$ 17,078	$ 16,888	$ 17,078
Expenses	3,346	3,713	3,348	3,359	3,723	3,999	3,616	3,739	11,838	12,201	8,795	15,077
Net income including noncontrolling interest	230	306	1,035	717	668	180	356	797	2,288	2,001	4,584	2,001
Net income attributable to common stock	174	300	1,016	698	649	161	337	778	2,188	1,925	4,508	1,925
Net income per common share(1):
Revenues and other	3,576	4,019	4,383	4,076	4,391	4,179	3,972	4,536	16,054	17,078	16,888	17,078
Expenses	3,346	3,713	3,348	3,359	3,723	3,999	3,616	3,739	11,838	12,201	8,795	15,077
Net income including noncontrolling interest	230	306	1,035	717	668	180	356	797	2,288	2,001	4,584	2,001
Net income attributable to common stock	$ 174	$ 300	$ 1,016	$ 698	$ 649	$ 161	$ 337	$ 778	$ 2,188	$ 1,925	$ 4,508	$ 1,925
Basic	$ 0.44	$ 0.75	$ 2.59	$ 1.78	$ 1.66	$ 0.41	$ 0.87	$ 2.02	$ 5.53	$ 4.95	$ 11.75	$ 4.95
Diluted	$ 0.43	$ 0.75	$ 2.54	$ 1.76	$ 1.64	$ 0.41	$ 0.86	$ 2.00	$ 5.50	$ 4.92	$ 11.47	$ 4.92