Quarterly Results of Operations (Unaudited) (Details) (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
Total revenues	$ 3,685	$ 3,411	$ 3,282	$ 3,176	$ 3,122	$ 3,009	$ 2,999	$ 2,839	$ 13,554	$ 11,969	$ 11,535
Total expenses	3,253	2,810	2,745	2,749	2,656	2,567	2,581	2,534	11,557	10,338	9,967
Income (loss) from continuing operations	348	439	398	329					1,514	1,244	1,286
Income (loss) from discontinued operations, net of federal income taxes	1								1		27
Net income (loss)	349	439	398	329	351	337	317	239	1,515	1,244	1,313
Earnings (loss) per common share - basic:
Income (loss) from continuing operations (in dollars per share)	$ 1.35	$ 1.69	$ 1.52	$ 1.25					$ 5.81	$ 4.68	$ 4.58
Income (loss) from discontinued operations (in dollars per share)											$ 0.10
Net income (loss) (in dollars per share)	$ 1.35	$ 1.69	$ 1.52	$ 1.25	$ 1.34	$ 1.28	$ 1.19	$ 0.89	$ 5.81	$ 4.68	$ 4.68
Earnings (loss) per common share - diluted:
Income (loss) from continuing operations (in dollars per share)	$ 1.32	$ 1.65	$ 1.48	$ 1.21					$ 5.67	$ 4.52	$ 4.47
Income (loss) from discontinued operations (in dollars per share)											$ 0.09
Net income (loss) (in dollars per share)	$ 1.32	$ 1.65	$ 1.48	$ 1.21	$ 1.29	$ 1.23	$ 1.15	$ 0.86	$ 5.67	$ 4.52	$ 4.56
Parent Company [Member]
Total revenues									918	849	783
Total expenses									325	333	306
Net income (loss)									$ 1,515	$ 1,244	$ 1,313