Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Results
Total revenues	$ 14,300	$ 11,457	$ 11,480	$ 11,413	$ 10,632	$ 10,372	$ 10,374	$ 10,428	$ 48,650	$ 41,806	$ 39,838
Income (loss) before income taxes	228	1,033	1,102	1,218	758	824	1,134	890	3,581	3,606	2,979
Shareholders' net income	$ 144	$ 772	$ 806	$ 915	$ 266	$ 560	$ 813	$ 598	$ 2,637	$ 2,237	$ 1,867
Shareholders' net income per share:
EPS, basic	$ 0.56	$ 3.18	$ 3.32	$ 3.78	$ 1.09	$ 2.25	$ 3.2	$ 2.34	$ 10.69	$ 8.92	$ 7.31
EPS, diluted	0.55	3.14	3.29	3.72	1.07	2.21	3.15	2.3	$ 10.54	$ 8.77	$ 7.19
Stock and Dividend Data
Price range of common stock - high	226.61	208.73	182.1	227.13	212.46	188.36	173.21	154.83
Price range of common stock - low	176.52	166.88	163.8	163.02	183.08	166.81	146.7	133.52
Dividends declared per share	$ 0	$ 0	$ 0	$ 0.04	$ 0	$ 0	$ 0	$ 0.04
Special items
U.S. tax reform	$ 3	$ (5)	$ 0	$ 0	$ 196	$ 0	$ 0	$ 0	$ (2)	$ 196
Debt extinguishment costs					0	209	0	0		209
Long-term care guaranty fund assessment					0	0	0	83		83
Transaction-related costs	402	108	109	50	25	6	(47)	49	669	$ 33	$ 147
Charges associated with litigation matters	(16)	35	0	0					$ 19		$ 25
Total special items	$ 389	$ 138	$ 109	$ 50	$ 221	$ 215	$ (47)	$ 132