Supplementary Insurance Information - Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 1,682	$ 1,216	$ 1,239
Reserves for future policy benefits, claims and unpaid losses and LAE	46,992	43,652	39,161
Unearned premiums	2,595	2,410	2,171
Net earned premiums	4,889	4,601	4,352
Net investment income	2,094	1,831	1,696
Benefits, claims, losses and settlement expenses	4,041	3,873	3,595
Amortization of deferred policy acquisition costs	860	690	673
Other operating expenses	1,610	1,578	1,443
Net written premiums (excluding life)	5,026	4,754	4,389
Property and casualty insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	299	270	238
Reserves for future policy benefits, claims and unpaid losses and LAE	9,741	9,678	8,563
Unearned premiums	2,595	2,410	2,171
Net earned premiums	4,865	4,579	4,328
Net investment income	438	362	350
Benefits, claims, losses and settlement expenses	3,003	2,955	2,762
Amortization of deferred policy acquisition costs	644	556	520
Other operating expenses	957	867	870
Net written premiums (excluding life)	5,023	4,751	4,386
Annuity
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	1,360	920	981
Reserves for future policy benefits, claims and unpaid losses and LAE	36,616	33,316	29,907
Net investment income	1,638	1,458	1,356
Benefits, claims, losses and settlement expenses	998	892	800
Amortization of deferred policy acquisition costs	212	130	149
Other operating expenses	174	159	142
Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	23	26	20
Reserves for future policy benefits, claims and unpaid losses and LAE	635	658	691
Net earned premiums	24	22	24
Net investment income	18	11	(10)
Benefits, claims, losses and settlement expenses	40	26	33
Amortization of deferred policy acquisition costs	4	4	4
Other operating expenses	479	552	431
Net written premiums (excluding life)	$ 3	$ 3	$ 3