Deferred Policy Acquisition Costs - Progression of deferred policy acquisition costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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	$ 1,216	$ 1,239
Deferred policy acquisition costs and present value of future profits, additions	219	207
Deferred policy acquisition costs and present value of future profits, periodic amortization	(230)	(185)
Deferred policy acquisition costs and present value of future profits, change included in realized gains	3	2
Deferred policy acquisition costs and present value of future profits, foreign currency translation	1	1
Deferred policy acquisition costs and present value of future profits, change in unrealized	208	(59)
Deferred policy acquisition costs and present value of future profits, ending balance	1,417	1,205
P&C
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred policy acquisition costs, beginning balance	270	238
Deferred policy acquisition costs, additions	162	139
Deferred policy acquisition costs, periodic amortization	(154)	(135)
Deferred policy acquisition costs, foreign currency translation	1	1
Deferred policy acquisition costs, ending balance	279	243
Annuity and Other
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred policy acquisition costs, beginning balance	1,217	1,110
Deferred policy acquisition costs, additions	57	67
Deferred policy acquisition costs, periodic amortization	(69)	(42)
Deferred policy acquisition costs, change included in realized gains	3	2
Deferred policy acquisition costs, ending balance	1,208	1,137
Movement in Deferred Sales Inducements [Roll Forward]
Deferred sales inducements, beginning balance	102	110
Deferred sales inducements, additions	0	1
Deferred sales inducements, periodic amortization	(5)	(6)
Deferred sales inducements, change included in realized gains	0	0
Deferred sales inducements, ending balance	97	105
Movement in Present Value of Future Insurance Profits [Roll Forward]
Present value of future profits, beginning balance	49	46
Present value of future profits, periodic amortization	(2)	(2)
Present value of future profits, ending balance	47	44
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	(422)	(265)
Unrealized investment gains (losses), change in unrealized	208	(59)
Unrealized investment gains (losses), ending balance	(214)	(324)
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	946	1,001
Deferred policy acquisition costs and present value of future profits, additions	57	68
Deferred policy acquisition costs and present value of future profits, periodic amortization	(76)	(50)
Deferred policy acquisition costs and present value of future profits, change included in realized gains	3	2
Deferred policy acquisition costs and present value of future profits, change in unrealized	208	(59)
Deferred policy acquisition costs and present value of future profits, ending balance	1,138	962
Excluding Unrealized Gains | Annuity and Other
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	1,368	1,266
Deferred policy acquisition costs and present value of future profits, change in unrealized	0	0
Deferred policy acquisition costs and present value of future profits, ending balance	$ 1,352	$ 1,286