Derivatives Derivatives (NQ, CF, FV) (Details) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Maximum Length of Time Hedged in Cash Flow Hedge	2 years		2 years
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	$ 10	$ (40)
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	(73)	(19)
Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	1	2
Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(350)	(892)
Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1)	(200)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	3	(34)
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Not Designated as Hedging Instrument [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Not Designated as Hedging Instrument [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(349)	(898)
Not Designated as Hedging Instrument [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1)	(200)
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(809)	(269)
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	(1)
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	3	(34)
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(41)	(20)
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(7)	6
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Equity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Equity Contract [Member] | Not Designated as Hedging Instrument [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Equity Contract [Member] | Not Designated as Hedging Instrument [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(44)	(938)
Equity Contract [Member] | Not Designated as Hedging Instrument [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	(184)
Embedded Derivative Financial Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Embedded Derivative Financial Instruments [Member] | Not Designated as Hedging Instrument [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Embedded Derivative Financial Instruments [Member] | Not Designated as Hedging Instrument [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	552	323
Embedded Derivative Financial Instruments [Member] | Not Designated as Hedging Instrument [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1)	(15)
Fair Value Hedging [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	7	2
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Fair Value Hedging [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Fair Value Hedging [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(8)	(2)
Fair Value Hedging [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	7	2
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	0	0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(8)	(2)
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Cash Flow Hedging [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	(8)
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	(73)	(19)
Cash Flow Hedging [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	1	2
Cash Flow Hedging [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	7	8
Cash Flow Hedging [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	0
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	(2)	0
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	1	2
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	7	0
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	(8)
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	(71)	(19)
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member] | Net investment income
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member] | Net Derivative Gain (Loss) [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	8
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member] | Policyholder benefits and claims
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 0	$ 0