Employee Benefit Plans (Estimated Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 8,750	$ 7,305	$ 7,390
Pension Benefits U.S. Plans [Member] | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,001	4,671
Pension Benefits U.S. Plans [Member] | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,718	2,003
Pension Benefits U.S. Plans [Member] | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	254	274
Pension Benefits U.S. Plans [Member] | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	735	685
Pension Benefits U.S. Plans [Member] | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,828	1,024
Pension Benefits U.S. Plans [Member] | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	270	206
Pension Benefits U.S. Plans [Member] | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	196	479
Pension Benefits U.S. Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,345	1,656
Pension Benefits U.S. Plans [Member] | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	951	1,224
Pension Benefits U.S. Plans [Member] | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	394	432
Pension Benefits U.S. Plans [Member] | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	767	563
Pension Benefits U.S. Plans [Member] | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	462	339
Pension Benefits U.S. Plans [Member] | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	85	13
Pension Benefits U.S. Plans [Member] | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	90	63
Pension Benefits U.S. Plans [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,179	2,430
Pension Benefits U.S. Plans [Member] | Level 1 | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,605	868
Pension Benefits U.S. Plans [Member] | Level 1 | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 1 | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 1 | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,605	868
Pension Benefits U.S. Plans [Member] | Level 1 | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 1 | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 1 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,345	1,496
Pension Benefits U.S. Plans [Member] | Level 1 | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	951	1,064
Pension Benefits U.S. Plans [Member] | Level 1 | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	394	432
Pension Benefits U.S. Plans [Member] | Level 1 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 1 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	189	49
Pension Benefits U.S. Plans [Member] | Level 1 | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29	1
Pension Benefits U.S. Plans [Member] | Level 1 | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	16
Pension Benefits U.S. Plans [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,651	4,056
Pension Benefits U.S. Plans [Member] | Level 2 | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,291	3,719
Pension Benefits U.S. Plans [Member] | Level 2 | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,638	1,948
Pension Benefits U.S. Plans [Member] | Level 2 | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	254	274
Pension Benefits U.S. Plans [Member] | Level 2 | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	718	675
Pension Benefits U.S. Plans [Member] | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	223	156
Pension Benefits U.S. Plans [Member] | Level 2 | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	270	206
Pension Benefits U.S. Plans [Member] | Level 2 | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	188	460
Pension Benefits U.S. Plans [Member] | Level 2 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	21
Pension Benefits U.S. Plans [Member] | Level 2 | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	21
Pension Benefits U.S. Plans [Member] | Level 2 | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 2 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24	0
Pension Benefits U.S. Plans [Member] | Level 2 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	273	290
Pension Benefits U.S. Plans [Member] | Level 2 | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	56	12
Pension Benefits U.S. Plans [Member] | Level 2 | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	14
Pension Benefits U.S. Plans [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	920	819
Pension Benefits U.S. Plans [Member] | Level 3 | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105	84
Pension Benefits U.S. Plans [Member] | Level 3 | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	80	55	18	30
Pension Benefits U.S. Plans [Member] | Level 3 | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 3 | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	10	7	5
Pension Benefits U.S. Plans [Member] | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 3 | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 3 | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	19	7	2
Pension Benefits U.S. Plans [Member] | Level 3 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	139
Pension Benefits U.S. Plans [Member] | Level 3 | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	139	129	194
Pension Benefits U.S. Plans [Member] | Level 3 | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 3 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	743	563	419	501
Pension Benefits U.S. Plans [Member] | Level 3 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 3 | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits U.S. Plans [Member] | Level 3 | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	72	33	1	4
Other Postretirement Benefits U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,426	1,352	1,320
Other Postretirement Benefits U.S. Plans [Member] | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	710	608
Other Postretirement Benefits U.S. Plans [Member] | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	289	248
Other Postretirement Benefits U.S. Plans [Member] | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35	33
Other Postretirement Benefits U.S. Plans [Member] | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	68	63
Other Postretirement Benefits U.S. Plans [Member] | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	181	140
Other Postretirement Benefits U.S. Plans [Member] | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	74	70
Other Postretirement Benefits U.S. Plans [Member] | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63	54
Other Postretirement Benefits U.S. Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	268	298
Other Postretirement Benefits U.S. Plans [Member] | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	188	196
Other Postretirement Benefits U.S. Plans [Member] | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	80	102
Other Postretirement Benefits U.S. Plans [Member] | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	447	439
Other Postretirement Benefits U.S. Plans [Member] | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	4
Other Postretirement Benefits U.S. Plans [Member] | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	3
Other Postretirement Benefits U.S. Plans [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	493	569
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	211	267
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42	77
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	169	135
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	55
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	268	298
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	188	196
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	80	102
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	0
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	4
Other Postretirement Benefits U.S. Plans [Member] | Level 1 | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	930	782
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	496	340
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	244	170
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35	33
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	68	63
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12	5
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	74	15
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63	54
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	433	439
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 2 | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	3
Other Postretirement Benefits U.S. Plans [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	1
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	1
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Corporate fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	1	4	4
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Federal agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Foreign government
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Municipals securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	1	1
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	3	5
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Common stock - domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Common stock - foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits U.S. Plans [Member] | Level 3 | Derivative assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0	$ 0	$ 1