Fair Value - Separate Accounts Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	$ 4,074	$ 3,884
Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	3,846	3,693
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	3,428	3,286
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	3	3
Common/Collective Trusts [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	415	404
Cash and Cash Equivalents [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	228	191
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	983	782
Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	983	782
Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	0	0
Fair Value, Inputs, Level 1 [Member] | Common/Collective Trusts [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	0	0
Level 2 | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	2,863	2,907
Level 2 | Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	2,445	2,500
Level 2 | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	3	3
Level 2 | Common/Collective Trusts [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	415	404
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	0	4
Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	0	4
Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	0	0
Fair Value, Inputs, Level 3 [Member] | Common/Collective Trusts [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account assets	$ 0	$ 0