Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Mortgage loans		$ 1,073	$ 1,068
Policy loans		170	174
Financial liabilities:
Long-term debt		1,423	1,302
Level 1
Financial assets:
Cash and cash equivalents		2,374	1,515
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		2,374	1,515
Financial liabilities:
Annuity benefits accumulated	[1]	0	0
Long-term debt		0	0
Total financial liabilities not accounted for at fair value		0	0
Level 2
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		0	0
Financial liabilities:
Annuity benefits accumulated	[1]	0	0
Long-term debt		1,479	1,228
Total financial liabilities not accounted for at fair value		1,479	1,228
Level 3
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		1,080	1,056
Policy loans		170	174
Total financial assets not accounted for at fair value		1,250	1,230
Financial liabilities:
Annuity benefits accumulated	[1]	38,634	34,765
Long-term debt		3	3
Total financial liabilities not accounted for at fair value		38,637	34,768
Carrying Value
Financial assets:
Cash and cash equivalents		2,374	1,515
Mortgage loans		1,073	1,068
Policy loans		170	174
Total financial assets not accounted for at fair value		3,617	2,757
Financial liabilities:
Annuity benefits accumulated	[1]	38,806	36,384
Long-term debt		1,423	1,302
Total financial liabilities not accounted for at fair value		40,229	37,686
Fair Value
Financial assets:
Cash and cash equivalents		2,374	1,515
Mortgage loans		1,080	1,056
Policy loans		170	174
Total financial assets not accounted for at fair value		3,624	2,745
Financial liabilities:
Annuity benefits accumulated	[1]	38,634	34,765
Long-term debt		1,482	1,231
Total financial liabilities not accounted for at fair value		$ 40,116	$ 35,996

[1] Excludes $238 million and $232 million of life contingent annuities in the payout phase at June 30, 2019 and December 31, 2018, respectively.