Investments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Gain (Loss) on Securities [Line Items]
Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments	$ 1,458		$ 1,078
Derivative, notional amount	174		172
Derivative liability	(2)
Derivative asset, fair value, gross asset			$ 4
Future capital call commitments for limited partnership investments	597
Mortgage loan commitments	9
Commitments to purchase or fund privately placed debt securities	283
Commitments to sell various privately placed debt securities	150
Common Stock
Gain (Loss) on Securities [Line Items]
Equity securities, FV-NI, gain (loss)	17	$ 1
Preferred stock
Gain (Loss) on Securities [Line Items]
Equity securities, FV-NI, gain (loss)	$ 42	$ (15)