Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Total revenues	$ 3,171	$ 3,716	$ 3,381	$ 3,304	$ 3,685	$ 3,411	$ 3,282	$ 3,176	$ 13,572	$ 13,554	$ 11,969
Total expenses	2,820	3,448	2,932	2,942	3,253	2,810	2,745	2,749	12,142	11,557	10,338
Income (loss) from continuing operations					348	439	398	329	1,154	1,514	1,244
Income (loss) from discontinued operations, net of federal income tax expense (benefit)					1					1
Net income (loss)	$ 283	$ 227	$ 344	$ 300	$ 349	$ 439	$ 398	$ 329	$ 1,154	$ 1,515	$ 1,244
Earnings (loss) per common share - basic:
Income (loss) from continuing operations (in dollars per share)					$ 1.35	$ 1.69	$ 1.52	$ 1.25	$ 4.60	$ 5.81	$ 4.68
Net income (loss) (in dollars per share)	$ 1.15	$ 0.91	$ 1.37	$ 1.17	1.35	1.69	1.52	1.25	4.60	5.81	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	4.51	5.67	4.52
Net income (loss) (in dollars per share)	$ 1.14	$ 0.87	$ 1.35	$ 1.15	$ 1.32	$ 1.65	$ 1.48	$ 1.21	$ 4.51	$ 5.67	$ 4.52
Parent Company [Member]
Total revenues									$ 1,311	$ 918	$ 849
Total expenses									315	325	333
Net income (loss)									$ 1,154	$ 1,515	$ 1,244