Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Mortgage loans		$ 1,078	$ 1,068
Policy loans		172	174
Financial liabilities:
Long-term debt		1,423	1,302
Level 1
Financial assets:
Cash and cash equivalents		2,000	1,515
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		2,000	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		1,403	1,228
Total financial liabilities not accounted for at fair value		1,403	1,228
Level 3
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		1,071	1,056
Policy loans		172	174
Total financial assets not accounted for at fair value		1,243	1,230
Financial liabilities:
Annuity benefits accumulated	[1]	36,881	34,765
Long-term debt		3	3
Total financial liabilities not accounted for at fair value		36,884	34,768
Carrying Value
Financial assets:
Cash and cash equivalents		2,000	1,515
Mortgage loans		1,078	1,068
Policy loans		172	174
Total financial assets not accounted for at fair value		3,250	2,757
Financial liabilities:
Annuity benefits accumulated	[1]	37,768	36,384
Long-term debt		1,423	1,302
Total financial liabilities not accounted for at fair value		39,191	37,686
Fair Value
Financial assets:
Cash and cash equivalents		2,000	1,515
Mortgage loans		1,071	1,056
Policy loans		172	174
Total financial assets not accounted for at fair value		3,243	2,745
Financial liabilities:
Annuity benefits accumulated	[1]	36,881	34,765
Long-term debt		1,406	1,231
Total financial liabilities not accounted for at fair value		$ 38,287	$ 35,996

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