v3.19.3.a.u2
Financial Instruments (Gross Unrealized Losses and Fair Values for Investments in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Investments, Unrealized Loss Position [Line Items]    
Less than 12 Months, Fair Value $ 12,953 $ 27,724
Less than 12 Months, Unrealized Loss (35) (267)
12 Months or Greater, Fair Value 8,403 43,941
12 Months or Greater, Unrealized Loss (39) (787)
Total Fair Value 21,356 71,665
Total Unrealized Loss (74) (1,054)
Government bonds    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 Months, Fair Value 6,752 12,019
Less than 12 Months, Unrealized Loss (20) (85)
12 Months or Greater, Fair Value 4,590 23,877
12 Months or Greater, Unrealized Loss (10) (329)
Total Fair Value 11,342 35,896
Total Unrealized Loss (30) (414)
Corporate debt securities    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 Months, Fair Value 1,665 10,171
Less than 12 Months, Unrealized Loss (2) (107)
12 Months or Greater, Fair Value 978 11,545
12 Months or Greater, Unrealized Loss (1) (209)
Total Fair Value 2,643 21,716
Total Unrealized Loss (3) (316)
Mortgage-backed and asset-backed securities    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 Months, Fair Value 4,536 5,534
Less than 12 Months, Unrealized Loss (13) (75)
12 Months or Greater, Fair Value 2,835 8,519
12 Months or Greater, Unrealized Loss (28) (249)
Total Fair Value 7,371 14,053
Total Unrealized Loss $ (41) $ (324)