Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Mortgage loans		$ 1,147	$ 1,067
Policy loans		192	201
Financial liabilities:
Long-term debt		1,283	998
Level 1
Financial assets:
Cash and cash equivalents		2,107	1,220
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		2,107	1,220
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		1,353	1,105
Total financial liabilities not accounted for at fair value		1,353	1,105
Level 3
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		1,146	1,074
Policy loans		192	201
Total financial assets not accounted for at fair value		1,338	1,275
Financial liabilities:
Annuity benefits accumulated	[1]	28,932	25,488
Long-term debt		3	15
Total financial liabilities not accounted for at fair value		28,935	25,503
Carrying Value
Financial assets:
Cash and cash equivalents		2,107	1,220
Mortgage loans		1,147	1,067
Policy loans		192	201
Total financial assets not accounted for at fair value		3,446	2,488
Financial liabilities:
Annuity benefits accumulated	[1]	29,703	26,422
Long-term debt		1,284	1,000
Total financial liabilities not accounted for at fair value		30,987	27,422
Fair Value
Financial assets:
Cash and cash equivalents		2,107	1,220
Mortgage loans		1,146	1,074
Policy loans		192	201
Total financial assets not accounted for at fair value		3,445	2,495
Financial liabilities:
Annuity benefits accumulated	[1]	28,932	25,488
Long-term debt		1,356	1,120
Total financial liabilities not accounted for at fair value		$ 30,288	$ 26,608

[1] Excludes $204 million and $200 million of life contingent annuities in the payout phase at December 31, 2016 and 2015, respectively.