Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Financial assets:
Mortgage loans		$ 1,043	$ 1,147
Policy loans		186	192
Financial liabilities:
Long-term debt		1,284	1,283
Level 1
Financial assets:
Cash and cash equivalents		2,349	2,107
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		2,349	2,107
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		1,377	1,353
Total financial liabilities not accounted for at fair value		1,377	1,353
Level 3
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		1,040	1,146
Policy loans		186	192
Total financial assets not accounted for at fair value		1,226	1,338
Financial liabilities:
Annuity benefits accumulated	[1]	31,857	28,932
Long-term debt		3	3
Total financial liabilities not accounted for at fair value		31,860	28,935
Carrying Value
Financial assets:
Cash and cash equivalents		2,349	2,107
Mortgage loans		1,043	1,147
Policy loans		186	192
Total financial assets not accounted for at fair value		3,578	3,446
Financial liabilities:
Annuity benefits accumulated	[1]	32,464	29,703
Long-term debt		1,284	1,284
Total financial liabilities not accounted for at fair value		33,748	30,987
Fair Value
Financial assets:
Cash and cash equivalents		2,349	2,107
Mortgage loans		1,040	1,146
Policy loans		186	192
Total financial assets not accounted for at fair value		3,575	3,445
Financial liabilities:
Annuity benefits accumulated	[1]	31,857	28,932
Long-term debt		1,380	1,356
Total financial liabilities not accounted for at fair value		$ 33,237	$ 30,288

[1] Excludes $207 million and $204 million of life contingent annuities in the payout phase at September 30, 2017 and December 31, 2016, respectively.