Selected Quarterly Financial Data (Unaudited) (details) (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
Selected Quarterly Financial Data (Unaudited) disclosure
Total revenues	$ 6,477	$ 6,512	$ 6,359	$ 6,392	$ 6,373	$ 6,407	$ 6,388	$ 6,278	$ 25,740	$ 25,446	$ 25,112
Total expenses	6,166	5,342	5,751	5,315	5,595	6,075	7,115	5,309	22,574	24,094	20,806
Income before income taxes	311	1,170	608	1,077	778	332	(727)	969	3,166	1,352	4,306
Income tax expense (benefit)	7	306	109	271	160	(1)	(363)	130	693	(74)	1,090
Net income	$ 304	$ 864	$ 499	$ 806	$ 618	$ 333	$ (364)	$ 839	$ 2,473	$ 1,426	$ 3,216
Net income (loss) per share, basic	$ 0.79	$ 2.23	$ 1.27	$ 2.04	$ 1.52	$ 0.80	$ (0.88)	$ 1.94	$ 6.35	$ 3.40	$ 6.69
Net income (loss) per share, diluted	$ 0.78	$ 2.21	$ 1.26	$ 2.02	$ 1.51	$ 0.79	$ (0.88)	$ 1.92	$ 6.30	$ 3.36	$ 6.62