Schedule II-Condensed Financial Information Of Registrant (Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 3,934	$ 3,609	$ 4,075	$ 2,113
Fixed maturity securities (Parent Company - amortized cost of $589 and $342)	16,692	17,377
Other invested assets, current	21	17
Other receivables	2,558	2,267
Income taxes receivable	10	342
Securities lending collateral	604	455
Other current assets	2,104	2,249
Total current assets	34,321	36,263
Fixed maturity securities (Parent Company - amortized cost $0)	487	561
Other invested assets, long-term	3,726	3,344
Property and equipment, net	2,735	2,175
Other noncurrent assets	758	565
Total assets	71,571	70,540
Current liabilities:
Accounts payable and accrued expenses	4,959	5,024
Security trades pending payable	197	113
Securities lending payable	604	454
Current portion of long-term debt	849	1,275
Other current liabilities	3,190	3,343
Total current liabilities	21,965	23,356
Long-term debt, less current portion	17,217	17,382
Other noncurrent liabilities	1,182	925
Total liabilities	43,030	44,037
Commitments and contingencies-Note 5
Shareholders' equity
Preferred stock, without par value, shares authorized - 100,000,000; shares issued and outstanding - none	0	0
Common stock, par value $0.01, shares authorized - 900,000,000; shares issued and outstanding - 257,395,577 and 256,084,913	3	3
Additional paid-in capital	9,536	8,547
Retained earnings	19,988	18,054
Accumulated other comprehensive loss	(986)	(101)
Total shareholders' equity	28,541	26,503	25,101	23,045
Total liabilities and shareholders' equity	71,571	70,540
Parent Company [Member]
Current assets:
Cash and cash equivalents	1,290	956	$ 883	$ 493
Fixed maturity securities (Parent Company - amortized cost of $589 and $342)	573	346
Equity securities, current	86	1,458
Other invested assets, current	10	5
Other receivables	131	61
Income taxes receivable	0	75
Net due from subsidiaries	170	2,428
Securities lending collateral	35	15
Other current assets	320	228
Total current assets	2,615	5,572
Equity securities	6	6
Other invested assets, long-term	616	644
Property and equipment, net	186	118
Deferred tax assets, net	209	162
Investment in subsidiaries	44,877	40,211
Other noncurrent assets	225	89
Total assets	48,734	46,802
Current liabilities:
Accounts payable and accrued expenses	1,429	1,232
Security trades pending payable	0	11
Securities lending payable	35	14
Income taxes payable	112	0
Current portion of long-term debt	849	1,275
Other current liabilities	235	219
Total current liabilities	2,660	2,751
Long-term debt, less current portion	17,192	17,357
Other noncurrent liabilities	341	191
Total liabilities	20,193	20,299
Commitments and contingencies-Note 5
Shareholders' equity
Preferred stock, without par value, shares authorized - 100,000,000; shares issued and outstanding - none	0	0
Common stock, par value $0.01, shares authorized - 900,000,000; shares issued and outstanding - 257,395,577 and 256,084,913	3	3
Additional paid-in capital	9,536	8,547
Retained earnings	19,988	18,054
Accumulated other comprehensive loss	(986)	(101)
Total shareholders' equity	28,541	26,503
Total liabilities and shareholders' equity	$ 48,734	$ 46,802