Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total revenues	$ 4,344	$ 4,638	$ 4,310	$ 3,965	$ 4,531	$ 4,264	$ 4,020	$ 3,609	$ 17,258	$ 16,424	$ 14,257
Total expenses	3,863	4,888	3,889	3,697	4,064	3,732	3,569	3,174	16,339	14,539	13,127
Net income (loss)	$ 431	$ (161)	$ 363	$ 252	$ 399	$ 490	$ 385	$ 367	$ 886	$ 1,641	$ 2,079
Earnings (loss) per common share - basic:
Net income (loss) (in dollars per share)	$ 2.18	$ (0.81)	$ 1.80	$ 1.23	$ 1.89	$ 2.27	$ 1.76	$ 1.68	$ 4.41	$ 7.60	$ 9.36
Earnings (loss) per common share - diluted:
Net income (loss) (in dollars per share)	$ 2.15	$ (0.83)	$ 1.79	$ 1.22	$ 1.80	$ 2.24	$ 1.70	$ 1.64	$ 4.38	$ 7.40	$ 9.22
Parent Company [Member]
Total revenues									$ 1,001	$ 1,183	$ 1,201
Total expenses									410	340	308
Net income (loss)									$ 886	$ 1,641	$ 2,079