Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Financial assets:
Mortgage loans		$ 1,159	$ 1,147
Policy loans		190	192
Financial liabilities:
Long-term debt		1,283	1,283
Level 1
Financial assets:
Cash and cash equivalents		1,890	2,107
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		1,890	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		1,379	1,353
Total financial liabilities not accounted for at fair value		1,379	1,353
Level 3
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		1,158	1,146
Policy loans		190	192
Total financial assets not accounted for at fair value		1,348	1,338
Financial liabilities:
Annuity benefits accumulated	[1]	29,997	28,932
Long-term debt		3	3
Total financial liabilities not accounted for at fair value		30,000	28,935
Carrying Value
Financial assets:
Cash and cash equivalents		1,890	2,107
Mortgage loans		1,159	1,147
Policy loans		190	192
Total financial assets not accounted for at fair value		3,239	3,446
Financial liabilities:
Annuity benefits accumulated	[1]	30,799	29,703
Long-term debt		1,283	1,284
Total financial liabilities not accounted for at fair value		32,082	30,987
Fair Value
Financial assets:
Cash and cash equivalents		1,890	2,107
Mortgage loans		1,158	1,146
Policy loans		190	192
Total financial assets not accounted for at fair value		3,238	3,445
Financial liabilities:
Annuity benefits accumulated	[1]	29,997	28,932
Long-term debt		1,382	1,356
Total financial liabilities not accounted for at fair value		$ 31,379	$ 30,288

[1] Excludes $203 million and $204 million of life contingent annuities in the payout phase at March 31, 2017 and December 31, 2016, respectively.