Derivative Instruments - Summary of Notional and Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Total derivative assets	$ 2,757	$ 2,863
Total derivative liabilities	8,783	7,592
Derivatives designated as hedges
Derivative [Line Items]
Derivative assets, fair value	31	1
Derivative liabilities, fair value	98	99
Derivatives designated as hedges | Foreign currency swaps
Derivative [Line Items]
Notional Amount	1,832	928
Derivative assets, fair value	31	1
Derivative liabilities, fair value	98	99
Derivatives designated as hedges | Interest rate swaps
Derivative [Line Items]
Notional Amount	0	302
Derivative assets, fair value	0	0
Derivative liabilities, fair value	0	0
Derivatives not designated as hedges
Derivative [Line Items]
Total derivative assets	2,726	2,862
Total derivative liabilities	8,685	7,493
Derivatives not designated as hedges | Foreign currency swaps
Derivative [Line Items]
Notional Amount	38	41
Derivative assets, fair value	3	21
Derivative liabilities, fair value	3	3
Derivatives not designated as hedges | Interest rate swaps
Derivative [Line Items]
Notional Amount	451	385
Derivative assets, fair value	0	0
Derivative liabilities, fair value	1	2
Derivatives not designated as hedges | Equity options
Derivative [Line Items]
Notional Amount	38,381	31,460
Derivative assets, fair value	2,468	2,500
Derivative liabilities, fair value	15	19
Derivatives not designated as hedges | Futures
Derivative [Line Items]
Notional Amount	3	1,134
Derivative assets, fair value	5	7
Derivative liabilities, fair value	0	0
Derivatives not designated as hedges | Total return swaps
Derivative [Line Items]
Notional Amount	62	114
Derivative assets, fair value	2	5
Derivative liabilities, fair value	0	0
Derivatives not designated as hedges | Credit default swaps
Derivative [Line Items]
Notional Amount	10	10
Derivative assets, fair value	0	0
Derivative liabilities, fair value	4	5
Derivatives not designated as hedges | Foreign currency forwards
Derivative [Line Items]
Notional Amount	588	1,139
Derivative assets, fair value	6	17
Derivative liabilities, fair value	3	6
Derivatives not designated as hedges | Embedded derivatives | Funds withheld
Derivative [Line Items]
Notional Amount	0	0
Embedded derivative assets, fair value		312
Embedded derivative liabilities, fair value		22
Derivatives not designated as hedges | Embedded derivatives | Interest sensitive contract liabilities
Derivative [Line Items]
Notional Amount	0	0
Embedded derivative assets, fair value	0	0
Embedded derivative liabilities, fair value	8,656	7,436
Consolidated Entity Excluding Variable Interest Entities (VIE)
Derivative [Line Items]
Funds withheld liability	389	407
Derivative liabilities, fair value	124	134
Consolidated Entity Excluding Variable Interest Entities (VIE) | Derivatives not designated as hedges | Embedded derivatives | Funds withheld
Derivative [Line Items]
Funds withheld at interest	242
Funds withheld liability	3
Consolidated Entity Excluding Variable Interest Entities (VIE) | Level 3 | Recurring
Derivative [Line Items]
Derivative assets, fair value	0	0
Derivative liabilities, fair value	4	5
Consolidated Entity Excluding Variable Interest Entities (VIE) | Level 3 | Recurring | Embedded derivatives
Derivative [Line Items]
Funds withheld at interest	151	312
Funds withheld liability	0	0
Consolidated Entity Excluding Variable Interest Entities (VIE) | Level 2 | Recurring
Derivative [Line Items]
Derivative assets, fair value	2,510	2,544
Derivative liabilities, fair value	120	129
Consolidated Entity Excluding Variable Interest Entities (VIE) | Level 2 | Recurring | Embedded derivatives
Derivative [Line Items]
Funds withheld at interest	0	0
Funds withheld liability	$ 3	$ 22