Derivatives (Primary Risks Managed by Derivatives) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative, Notional Amount	$ 92,676	$ 113,450
Derivative Asset, Fair Value, Gross Asset	2,765	2,244
Derivative Liability, Fair Value, Gross Liability	2,112	3,129
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	2,461	1,964
Derivative Asset, Fair Value, Gross Asset	200	135
Derivative Liability, Fair Value, Gross Liability	30	75
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	0	175
Derivative Asset, Fair Value, Gross Asset	0	44
Derivative Liability, Fair Value, Gross Liability	0	0
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Notional Amount	2,461	1,789
Derivative Asset, Fair Value, Gross Asset	200	91
Derivative Liability, Fair Value, Gross Liability	30	75
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	0	27
Derivative Asset, Fair Value, Gross Asset	0	5
Derivative Liability, Fair Value, Gross Liability	0	0
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Currency Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	2,461	1,762
Derivative Asset, Fair Value, Gross Asset	200	86
Derivative Liability, Fair Value, Gross Liability	30	75
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	90,215	111,486
Derivative Asset, Fair Value, Gross Asset	2,565	2,109
Derivative Liability, Fair Value, Gross Liability	2,082	3,054
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	10,747	20,213
Derivative Asset, Fair Value, Gross Asset	528	922
Derivative Liability, Fair Value, Gross Liability	558	774
Not Designated as Hedging Instrument [Member] | Currency Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,398	1,103
Derivative Asset, Fair Value, Gross Asset	99	69
Derivative Liability, Fair Value, Gross Liability	18	41
Not Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Derivative, Notional Amount	3,350	2,671
Derivative Asset, Fair Value, Gross Asset	21	7
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Futures [Member]
Derivative [Line Items]
Derivative, Notional Amount	53	282
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Interest Rate Swaption [Member]
Derivative [Line Items]
Derivative, Notional Amount	17,168	24,600
Derivative Asset, Fair Value, Gross Asset	168	133
Derivative Liability, Fair Value, Gross Liability	61	63
Not Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Derivative [Line Items]
Derivative, Notional Amount	125	130
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	2
Not Designated as Hedging Instrument [Member] | Credit Default Swap, Buying Protection [Member]
Derivative [Line Items]
Derivative, Notional Amount	98	65
Derivative Asset, Fair Value, Gross Asset	3	0
Derivative Liability, Fair Value, Gross Liability	0	1
Not Designated as Hedging Instrument [Member] | Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,798	1,878
Derivative Asset, Fair Value, Gross Asset	14	40
Derivative Liability, Fair Value, Gross Liability	3	0
Not Designated as Hedging Instrument [Member] | Equity Futures [Member]
Derivative [Line Items]
Derivative, Notional Amount	169	2,713
Derivative Asset, Fair Value, Gross Asset	0	15
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Equity Option [Member]
Derivative [Line Items]
Derivative, Notional Amount	45,815	47,066
Derivative Asset, Fair Value, Gross Asset	1,372	794
Derivative Liability, Fair Value, Gross Liability	1,207	1,664
Not Designated as Hedging Instrument [Member] | Variance Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	5,574	8,998
Derivative Asset, Fair Value, Gross Asset	80	128
Derivative Liability, Fair Value, Gross Liability	232	430
Not Designated as Hedging Instrument [Member] | Equity Total Return Swaps [Member]
Derivative [Line Items]
Derivative, Notional Amount	3,920	1,767
Derivative Asset, Fair Value, Gross Asset	280	0
Derivative Liability, Fair Value, Gross Liability	$ 3	$ 79