Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	[1]	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total revenues	$ 3,669		$ 3,511	$ 3,577	$ 3,500	$ 3,255		$ 3,525	$ 3,307	$ 3,243	$ 14,257	$ 13,330	$ 13,572
Total expenses	4,057		3,001	3,044	3,025	3,058		2,913	2,893	3,008	13,127	11,872	12,142
Net income (loss)	$ 816		$ 418	$ 411	$ 435	$ 189		$ 467	$ 325	$ 211	$ 2,079	$ 1,192	$ 1,154
Earnings (loss) per common share - basic:
Net income (loss) (in dollars per share)	$ 3.73		$ 1.89	$ 1.84	$ 1.93	$ 0.83		$ 2.02	$ 1.37	$ 0.87	$ 9.36	$ 5.09	$ 4.60
Earnings (loss) per common share - diluted:
Net income (loss) (in dollars per share)	$ 3.67		$ 1.87	$ 1.81	$ 1.89	$ 0.82		$ 2.00	$ 1.35	$ 0.83	$ 9.22	$ 5.03	$ 4.51
Parent Company [Member]
Total revenues											$ 1,201	$ 1,161	$ 1,311
Total expenses											308	389	315
Net income (loss)											$ 2,079	$ 1,192	$ 1,154

[1] Fourth quarter 2017 results include a goodwill impairment charge and the impacts of remeasuring our existing deferred tax balances for the impact of the Tax Act as disclosed elsewhere herein