Fair Value Measurements Fair Value Hierarchy for Assets and Liabilities Measured on a Recurring Basis (Details) | Mar. 31, 2018USD ($)firmprice | Dec. 31, 2017USD ($) |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | $ 1,782,000,000 | $ 1,816,000,000 |
Total assets | $ 1,782,000,000 | 2,816,000,000 |
Number of firms utilized | firm | 1 | |
U.S. government and agencies | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | $ 245,000,000 | 195,000,000 |
State and political subdivisions | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 230,000,000 | 391,000,000 |
Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 1,196,000,000 | 1,117,000,000 |
Mortgage-backed/asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 53,000,000 | 56,000,000 |
Foreign government bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 58,000,000 | 57,000,000 |
Preferred securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 316,000,000 | 319,000,000 |
Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | $ 677,000,000 | 681,000,000 |
Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Number of prices relied upon | price | 1 | |
Assets held at fair value | $ 0 | 0 |
Liabilities held at fair value | 0 | 0 |
Fair Value, Measurements, Recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 2,876,000,000 | 2,816,000,000 |
Fair Value, Measurements, Recurring | U.S. government and agencies | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 245,000,000 | 195,000,000 |
Fair Value, Measurements, Recurring | State and political subdivisions | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 230,000,000 | 391,000,000 |
Fair Value, Measurements, Recurring | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 1,196,000,000 | 1,117,000,000 |
Fair Value, Measurements, Recurring | Mortgage-backed/asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 53,000,000 | 56,000,000 |
Fair Value, Measurements, Recurring | Foreign government bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 58,000,000 | 57,000,000 |
Fair Value, Measurements, Recurring | Preferred securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 316,000,000 | 319,000,000 |
Fair Value, Measurements, Recurring | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 677,000,000 | 681,000,000 |
Fair Value, Measurements, Recurring | Other long-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 101,000,000 | |
Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 700,000,000 | 704,000,000 |
Fair Value, Measurements, Recurring | Level 1 | U.S. government and agencies | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | State and political subdivisions | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Mortgage-backed/asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Foreign government bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Preferred securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 23,000,000 | 23,000,000 |
Fair Value, Measurements, Recurring | Level 1 | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 677,000,000 | 681,000,000 |
Fair Value, Measurements, Recurring | Level 1 | Other long-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 0 | |
Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 2,062,000,000 | 2,112,000,000 |
Fair Value, Measurements, Recurring | Level 2 | U.S. government and agencies | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 245,000,000 | 195,000,000 |
Fair Value, Measurements, Recurring | Level 2 | State and political subdivisions | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 230,000,000 | 391,000,000 |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 1,183,000,000 | 1,117,000,000 |
Fair Value, Measurements, Recurring | Level 2 | Mortgage-backed/asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 53,000,000 | 56,000,000 |
Fair Value, Measurements, Recurring | Level 2 | Foreign government bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 58,000,000 | 57,000,000 |
Fair Value, Measurements, Recurring | Level 2 | Preferred securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 293,000,000 | 296,000,000 |
Fair Value, Measurements, Recurring | Level 2 | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 0 | 0 |
Fair Value, Measurements, Recurring | Level 2 | Other long-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 0 | |
Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 114,000,000 | 0 |
Fair Value, Measurements, Recurring | Level 3 | U.S. government and agencies | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | State and political subdivisions | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 13,000,000 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Mortgage-backed/asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Foreign government bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Preferred securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | 0 | $ 0 |
Fair Value, Measurements, Recurring | Level 3 | Other long-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available for sale, at fair value | $ 101,000,000 | |