Deferred Policy Acquisition Costs - Progression of deferred policy acquisition costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Deferred policy acquisition costs and present value of future profits, beginning balance	$ 1,205	$ 1,055	$ 1,239	$ 1,184
Deferred policy acquisition costs and present value of future profits, additions	218	197	425	402
Deferred policy acquisition costs and present value of future profits, periodic amortization	(178)	(168)	(363)	(334)
Deferred policy acquisition costs and present value of future profits, change included in realized gains	1	3	3	5
Deferred policy acquisition costs and present value of future profits, foreign currency translation	0	(1)	1	(1)
Deferred policy acquisition costs and present value of future profits, change in unrealized	(90)	(205)	(149)	(375)
Deferred policy acquisition costs and present value of future profits, ending balance	1,156	881	1,156	881
P&C
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred policy acquisition costs, beginning balance	243	224	238	226
Deferred policy acquisition costs, additions	151	139	290	271
Deferred policy acquisition costs, periodic amortization	(136)	(128)	(271)	(262)
Deferred policy acquisition costs, foreign currency translation	0	(1)	1	(1)
Deferred policy acquisition costs, ending balance	258	234	258	234
Annuity and Run-off Long-term Care and Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred policy acquisition costs, beginning balance	1,137	1,063	1,110	1,018
Deferred policy acquisition costs, additions	66	56	133	124
Deferred policy acquisition costs, periodic amortization	(36)	(32)	(78)	(57)
Deferred policy acquisition costs, change included in realized gains	0	2	2	4
Deferred policy acquisition costs, ending balance	1,167	1,089	1,167	1,089
Movement in Deferred Sales Inducements [Roll Forward]
Deferred sales inducements, beginning balance	105	119	110	119
Deferred sales inducements, additions	1	2	2	7
Deferred sales inducements, periodic amortization	(4)	(6)	(10)	(11)
Deferred sales inducements, change included in realized gains	1	1	1	1
Deferred sales inducements, ending balance	103	116	103	116
Movement in Present Value of Future Insurance Profits [Roll Forward]
Present value of future profits, beginning balance	44	53	46	55
Present value of future profits, periodic amortization	(2)	(2)	(4)	(4)
Present value of future profits, ending balance	42	51	42	51
Movement in Unrealized Gains (Losses) Related to Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Unrealized investment gains (losses), beginning balance	(324)	(404)	(265)	(234)
Unrealized investment gains (losses), change in unrealized	(90)	(205)	(149)	(375)
Unrealized investment gains (losses), ending balance	(414)	(609)	(414)	(609)
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Deferred policy acquisition costs and present value of future profits, beginning balance	962	831	1,001	958
Deferred policy acquisition costs and present value of future profits, additions	67	58	135	131
Deferred policy acquisition costs and present value of future profits, periodic amortization	(42)	(40)	(92)	(72)
Deferred policy acquisition costs and present value of future profits, change included in realized gains	1	3	3	5
Deferred policy acquisition costs and present value of future profits, change in unrealized	(90)	(205)	(149)	(375)
Deferred policy acquisition costs and present value of future profits, ending balance	898	647	898	647
Excluding Unrealized Gains | Annuity and Run-off Long-term Care and Life
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Deferred policy acquisition costs and present value of future profits, beginning balance	1,286	1,235	1,266	1,192
Deferred policy acquisition costs and present value of future profits, change in unrealized	0	0	0	0
Deferred policy acquisition costs and present value of future profits, ending balance	$ 1,312	$ 1,256	$ 1,312	$ 1,256