Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,025	$ 2,261
Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,236	1,357
Total limited partnerships measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	789	904
Corporate and other bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	482	532
Corporate and other bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate and other bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	472	522
Corporate and other bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	10
States, municipalities and political subdivisions
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	58	62
States, municipalities and political subdivisions | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
States, municipalities and political subdivisions | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	58	62
States, municipalities and political subdivisions | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Asset-backed
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165	180
Asset-backed | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Asset-backed | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165	180
Asset-backed | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total fixed maturity securities trading
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	705	774
Total fixed maturity securities trading | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total fixed maturity securities trading | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	695	764
Total fixed maturity securities trading | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	10
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	441
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	331
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	110
Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		527
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		405
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		122
Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Short term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	81	34
Short term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27	23
Short term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	54	11
Short term investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	9
Other assets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other assets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	9
Other assets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13
Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13
Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Total assets measured at fair value | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	358	441
Total assets measured at fair value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	868	906
Total assets measured at fair value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 10	$ 10