Claim and Claim Adjustment Expense Reserves Short Duration Contracts - Commercial Reconciliation (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 18,249	$ 18,576	$ 18,927	$ 19,117
Commercial - Auto [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	424
Commercial - General Liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,248
Commercial - Workers Compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	4,306
Commercial - Property and Other [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	327
Commercial [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 8,305	$ 8,576